Unblock startup of RabbitMQ during upgrade

RabbitMQ requires the hosts file to have addresses populated for
the host names it is expected to connect to, and without it spins
endlessly until restarted.

Changing the post-upgrade initialization sequence to invoke the
the hosts file generation script directly in the event that we stop
os-collect-config before it writes the file out.  This at some point
should be rewritten to be performed with a template or a new plugin.

Additionally placing an override file to short circuit the startup
wait which can seemingly get into a state where it never exits.

Change-Id: I7d03f4e08fd751a788fbe79782d253724f64fc9c