Support running periodic tasks immediately at startup

This change adds a parameter to allow periodic tasks that would
otherwise have to wait for a lengthy initial interval to run immediately
when the periodic tasks are started. This patch also applies the new
facility in the the _sync_power_states task in the compute manager to
get more timely access to Openstack server state when the compute node
starts up.

Change-Id: I461a5dbaa7d18919941ec31402910eef188d8e8c
Merge "Support running periodic tasks immediately at startup"