core: handle hot-set and update running vm

since the numOfSockets field was updateable, the infrastructure of
update-running-vm didn't take it into account,
when this was the only changed field, we had couple of issue:
1. the UI dialog didn't show, user cant choose if to apply now or later
2. next_run snapshot wasn't created

this fix is changine the field to updateableOnStatus, to handle above
issues, but since the user can choose if to use hot plug or not, a new
field introduced to the annotation, to mark fields that can be hot-set.

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1128443
Change-Id: I1c7f9b26ac4ddda6b446244b1fd85e2023809630
Signed-off-by: Omer Frenkel <ofrenkel@redhat.com>