Replace start_guests with resume_guests

Fuel UI offers an option to "start guests on reboot" which,
if set to true, will attempt to restart all guests on a
given host regardless of prior status. This commit changes
the nova.conf entry from start_guests_on_boot to
resume_guets_state_on_host_boot.

Change-Id: I3515c6350c1314cf091480ea109c8ade6195ea17
Partial-Bug: #1352284
Merge "Replace start_guests with resume_guests"