Description of problem:
Happened when install partitioning stage was happening on install of Fedora-Workstation-Live-x86_64-Rawhide-20160924.n.0.iso to a disk with existing partitions (chose to wipe them all, in guided partitioning).

Version-Release number of selected component:
anaconda-core-26.4-1.fc26.x86_64

The following was filed automatically by anaconda:
anaconda 26.4-1 exception report
Traceback (most recent call first):
  File "/usr/lib/python3.5/site-packages/blivet/formats/__init__.py", line 558, in _pre_destroy
    raise DeviceFormatError("device path does not exist or is not writable")
  File "/usr/lib/python3.5/site-packages/blivet/threads.py", line 45, in run_with_lock
    return m(*args, **kwargs)
  File "/usr/lib/python3.5/site-packages/blivet/formats/__init__.py", line 545, in destroy
    self._pre_destroy(**kwargs)
  File "/usr/lib/python3.5/site-packages/blivet/threads.py", line 45, in run_with_lock
    return m(*args, **kwargs)
  File "/usr/lib/python3.5/site-packages/blivet/deviceaction.py", line 700, in execute
    self.format.destroy()
  File "/usr/lib/python3.5/site-packages/blivet/threads.py", line 45, in run_with_lock
    return m(*args, **kwargs)
  File "/usr/lib/python3.5/site-packages/blivet/actionlist.py", line 325, in process
    action.execute(callbacks)
  File "/usr/lib/python3.5/site-packages/blivet/actionlist.py", line 48, in wrapped_func
    return func(obj, *args, **kwargs)
  File "/usr/lib/python3.5/site-packages/blivet/blivet.py", line 163, in do_it
    self.devicetree.actions.process(callbacks=callbacks, devices=self.devices)
  File "/usr/lib/python3.5/site-packages/blivet/threads.py", line 45, in run_with_lock
    return m(*args, **kwargs)
  File "/usr/lib/python3.5/site-packages/blivet/osinstall.py", line 1112, in turn_on_filesystems
    storage.do_it(callbacks)
  File "/usr/lib64/python3.5/site-packages/pyanaconda/install.py", line 204, in doInstall
    turn_on_filesystems(storage, mount_only=flags.flags.dirInstall, callbacks=callbacks_reg)
  File "/usr/lib64/python3.5/threading.py", line 862, in run
    self._target(*self._args, **self._kwargs)
  File "/usr/lib64/python3.5/site-packages/pyanaconda/threads.py", line 251, in run
    threading.Thread.run(self, *args, **kwargs)
blivet.errors.DeviceFormatError: device path does not exist or is not writable

Additional info:
addons:         com_redhat_kdump
cmdline:        /usr/bin/python3  /sbin/anaconda --liveinst --method=livecd:///dev/mapper/live-base
cmdline_file:   BOOT_IMAGE=vmlinuz initrd=initrd.img root=live:CDLABEL=Fedora-WS-Live-Rawhide-20160924- rd.live.image quiet
executable:     /sbin/anaconda
hashmarkername: anaconda
kernel:         4.8.0-0.rc7.git4.1.fc26.x86_64
other involved packages: system-python-libs-3.5.2-4.fc26.x86_64, python3-blivet-2.1.4-1.fc26.noarch
product:        Fedora
release:        Fedora release 26 (Rawhide)
type:           anaconda
version:        rawhide