Description of problem:
subscription-manager some "--config" option can use all kinds of characters when it should be a "number"

Version-Release number of selected component (if applicable):
subscription-manager-firstboot-1.13.19-1.el7.x86_64
subscription-manager-1.13.19-1.el7.x86_64
subscription-manager-gui-1.13.19-1.el7.x86_64
python-rhsm-1.13.10-1.el7.x86_64

How reproducible:
always

Steps to Reproduce:
1.run subscription-manager config --server.port=PORT
2.run subscription-manager config --rhsmcertd.autoattachinterval=PORT 

Actual results:
No errors report and when run "subscription-manager --config" I get output below
[server]
   hostname = subscription.rhn.stage.redhat.com
   insecure = [0]
   port = PORT      <==================should ONLY be a number
   prefix = [/subscription]
   proxy_hostname = []
   proxy_password = []
   proxy_port = []
   proxy_user = []
   ssl_verify_depth = [3]

[rhsm]
   baseurl = [https://cdn.redhat.com]
   ca_cert_dir = [/etc/rhsm/ca/]
   consumercertdir = [/etc/pki/consumer]
   entitlementcertdir = [/etc/pki/entitlement]
   full_refresh_on_yum = [0]
   manage_repos = [1]
   pluginconfdir = [/etc/rhsm/pluginconf.d]
   plugindir = [/usr/share/rhsm-plugins]
   productcertdir = [/etc/pki/product]
   repo_ca_cert = [/etc/rhsm/ca/redhat-uep.pem]
   report_package_profile = [1]

[rhsmcertd]
   autoattachinterval = PORT  <===========should ONLY be a number
   certcheckinterval = [240]

[] - Default value in use


Expected results:
when run 
subscription-manager config --server.port=PORT
there should be a error report like
"port must be 0-65535."
when run 
subscription-manager config --rhsmcertd.autoattachinterval=PORT
the error report should be
"Must enter a number"

Additional info:
I find that if you set some option that require "numbers" to a character the subscription-manager will use the default value of the option, that's good but I think we should not let the customer set a wrong option value.