Adds Support for Database Idle Timeout

Other OS services support the idle_timeout parameter that is
needed for reaping stale sql connections.  This is important for
clustered databases.

Conflicts:

        spec/classes/heat_init_spec.rb

Change-Id: Ia297410e61f246b2f5b4788b5d24961f070aa087
(cherry picked from commit 49f066e637fe22a25e80449cff8f0936682d7f10)