webadmin, core: enable edit Posix storage domains

Enable editing path of Posix storage domains via  UI.
Domains can be edited when in maintenance, the edited properties
are path, vfstype and mount options.

Change-Id: I8904ffab80e9d6e6bfdee4b8375872d1ff64b4d4
Signed-off-by: Alissa Bonas <abonas@redhat.com>