Description of problem:
I'm trying to create a VM in GNOME-Boxes, but all I get is an error in the GUI saying that it failed to create the VM. After asking on #boxes IRC, one user (toso) instructed me to run:

G_MESSAGES_DEBUG=Boxes gnome-boxes

resulting in:
(gnome-boxes:11971): Gtk-WARNING **: Theme parsing error: gtk-style.css:76:18: The 'outline-radius' property has been renamed to '-gtk-outline-radius'

(gnome-boxes:11971): Gtk-WARNING **: Theme parsing error: gtk-style.css:87:18: The 'outline-radius' property has been renamed to '-gtk-outline-radius'
(gnome-boxes:11971): Boxes-DEBUG: util-app.vala:199: Connected to system libvirt, now fetching domains..
(gnome-boxes:11971): Boxes-DEBUG: libvirt-system-importer.vala:69: Fetched 0 domains from system libvirt.
(gnome-boxes:11971): Boxes-DEBUG: wizard-source.vala:286: Nenhuma máquina para importar
(gnome-boxes:11971): Boxes-DEBUG: util-app.vala:292: check_cpu_vt_capability: sim
(gnome-boxes:11971): Boxes-DEBUG: util-app.vala:312: check_module_kvm_loaded: sim
(gnome-boxes:11971): Boxes-DEBUG: tracker-iso-query.vala:21: Tracker SPARQL query: SELECT nie:url(?iso)   nie:title(?iso)
       osinfo:id(?iso) osinfo:mediaId(?iso) osinfo:language(?iso)
{ ?iso nfo:isBootable true }

** (gnome-boxes:11971): WARNING **: Using a file (/usr/share/gnome-boxes/gnome-boxes-logos-db.xml) as a database location is deprecated, use a directory instead
(gnome-boxes:11971): Boxes-DEBUG: tracker-iso-query.vala:21: Tracker SPARQL query: SELECT nie:url(?iso)   nie:title(?iso)
       osinfo:id(?iso) osinfo:mediaId(?iso) osinfo:language(?iso)
{ ?iso nfo:isBootable true }
(gnome-boxes:11971): Boxes-DEBUG: vm-creator.vala:290: Creating volume 'boxes-unknown'..

(gnome-boxes:11971): Boxes-WARNING **: wizard.vala:465: Failed to create volume: internal error: unable to parse qemu-img output ''
(gnome-boxes:11971): Boxes-DEBUG: tracker-iso-query.vala:21: Tracker SPARQL query: SELECT nie:url(?iso)   nie:title(?iso)
       osinfo:id(?iso) osinfo:mediaId(?iso) osinfo:language(?iso)
{ ?iso nfo:isBootable true }
(gnome-boxes:11971): Boxes-DEBUG: tracker-iso-query.vala:21: Tracker SPARQL query: SELECT nie:url(?iso)   nie:title(?iso)
       osinfo:id(?iso) osinfo:mediaId(?iso) osinfo:language(?iso)
{ ?iso nfo:isBootable true }
(gnome-boxes:11971): Boxes-DEBUG: app.vala:477: Suspending running boxes
(gnome-boxes:11971): Boxes-DEBUG: app.vala:505: Running boxes suspended
[gustavo@fedora ~]$  G_MESSAGES_DEBUG=Boxes gnome-boxes

(gnome-boxes:12221): Gtk-WARNING **: Theme parsing error: gtk-style.css:76:18: The 'outline-radius' property has been renamed to '-gtk-outline-radius'

(gnome-boxes:12221): Gtk-WARNING **: Theme parsing error: gtk-style.css:87:18: The 'outline-radius' property has been renamed to '-gtk-outline-radius'
(gnome-boxes:12221): Boxes-DEBUG: util-app.vala:199: Connected to system libvirt, now fetching domains..
(gnome-boxes:12221): Boxes-DEBUG: util-app.vala:292: check_cpu_vt_capability: sim
(gnome-boxes:12221): Boxes-DEBUG: libvirt-system-importer.vala:69: Fetched 0 domains from system libvirt.
(gnome-boxes:12221): Boxes-DEBUG: wizard-source.vala:286: Nenhuma máquina para importar
(gnome-boxes:12221): Boxes-DEBUG: util-app.vala:312: check_module_kvm_loaded: sim

** (gnome-boxes:12221): WARNING **: Using a file (/usr/share/gnome-boxes/gnome-boxes-logos-db.xml) as a database location is deprecated, use a directory instead
(gnome-boxes:12221): Boxes-DEBUG: tracker-iso-query.vala:21: Tracker SPARQL query: SELECT nie:url(?iso)   nie:title(?iso)
       osinfo:id(?iso) osinfo:mediaId(?iso) osinfo:language(?iso)
{ ?iso nfo:isBootable true }


Version-Release number of selected component (if applicable):
I am on the latest version of this application in the time of the post.
Name        : gnome-boxes
Version     : 3.20.2
Release     : 4.fc24
Architecture: x86_64
Install Date: Sáb 02 Jul 2016 12:29:32 BRT
Group       : Applications/Emulators
Size        : 5145227
License     : LGPLv2+
Signature   : RSA/SHA256, Sex 24 Jun 2016 13:59:03 BRT, Key ID 73bde98381b46521
Source RPM  : gnome-boxes-3.20.2-4.fc24.src.rpm
Build Date  : Qui 23 Jun 2016 12:30:09 BRT
Build Host  : buildvm-04.phx2.fedoraproject.org
Relocations : (not relocatable)
Packager    : Fedora Project
Vendor      : Fedora Project
URL         : https://wiki.gnome.org/Apps/Boxes
Summary     : A simple GNOME 3 application to access remote or virtual systems
Description :
gnome-boxes lets you easily create, setup, access, and use:
  * remote machines
  * remote virtual machines
  * local virtual machines
  * When technology permits, set up access for applications on
    local virtual machines


How reproducible:
Everytime I run into the same problem, never getting past create VM phase.


Steps to Reproduce:
1. Open Boxes
2. Try to create a VM from an iso file
3. Fail

Actual results:
After opening the program using the command above, and clicking on adding a VM and creat, these are the results from terminal:

** (gnome-boxes:12430): WARNING **: Using a file (/usr/share/gnome-boxes/gnome-boxes-logos-db.xml) as a database location is deprecated, use a directory instead
(gnome-boxes:12430): Boxes-DEBUG: tracker-iso-query.vala:21: Tracker SPARQL query: SELECT nie:url(?iso)   nie:title(?iso)
       osinfo:id(?iso) osinfo:mediaId(?iso) osinfo:language(?iso)
{ ?iso nfo:isBootable true }
(gnome-boxes:12430): Boxes-DEBUG: vm-creator.vala:290: Creating volume 'boxes-unknown'..
(gnome-boxes:12430): Boxes-DEBUG: vm-creator.vala:292: Created volume 'boxes-unknown'.
(gnome-boxes:12430): Boxes-DEBUG: vm-configurator.vala:290: Using IDE controller for the main disk
(gnome-boxes:12430): Boxes-DEBUG: util-app.vala:162: Interface 'virbr0' is either not available or not up.
(gnome-boxes:12430): Boxes-DEBUG: vm-configurator.vala:482: Adding user network to (null)
(gnome-boxes:12430): Boxes-DEBUG: libvirt-machine.vala:165: new libvirt machine: boxes-unknown
(gnome-boxes:12430): Boxes-DEBUG: machine.vala:114: State of 'Fedora-Workstation-Live-x86_64-24-1' changed to BOXES_MACHINE_MACHINE_STATE_STOPPED
(gnome-boxes:12430): Boxes-DEBUG: libvirt-broker.vala:130: New domain 'boxes-unknown'
(gnome-boxes:12430): Boxes-DEBUG: util-app.vala:162: Interface 'virbr0' is either not available or not up.
(gnome-boxes:12430): Boxes-DEBUG: vm-configurator.vala:482: Adding user network to boxes-unknown
(gnome-boxes:12430): Boxes-DEBUG: tracker-iso-query.vala:21: Tracker SPARQL query: SELECT nie:url(?iso)   nie:title(?iso)
       osinfo:id(?iso) osinfo:mediaId(?iso) osinfo:language(?iso)
{ ?iso nfo:isBootable true }

(gnome-boxes:12430): Boxes-WARNING **: machine.vala:606: Failed to start Fedora-Workstation-Live-x86_64-24-1: Unable to start domain: Failed to connect socket to '/run/user/1000/libvirt/virtlogd-sock': No such file or directory


Expected results:
A working VM.


Additional info:
My system is updated.