frontend: Allow enabling/disabling SSO

This small feature allows controlling SSO per VM.
Changes:
 - new radio buttons in New/Edit VM/Template/VmPool dialog.

Change-Id: I213110a1554cd67b6cd8560477b5d7551e89f24e
Signed-off-by: Frantisek Kobzik <fkobzik@redhat.com>
Bug-Url: https://bugzilla.redhat.com/1035279