machine: Go to COLLECTION from explicit states only

When the machine disconnects and UIState is CREDS or DISPLAY we want to
return to COLLECTION view. However in some other states, like WIZARD
this doesnt make sense. This is why we shouldnt just exclude PROPERTIES
state from the affected comparision.

https://bugzilla.gnome.org/show_bug.cgi?id=736140
machine: Update screenshot on machine disconnect

If a machine disconnects we want to update the screenshot so if the user
is at the properties view he will get an indication that it is no longer
running.

https://bugzilla.gnome.org/show_bug.cgi?id=736140
properties-toolbar: Return to COLLECTION if VM is not running

https://bugzilla.gnome.org/show_bug.cgi?id=736140