Docs: include all useful module docs
Docs: include all useful module docs

The list of modules to exclude from autodoc was set some time back, and
is pretty arbitrary looking. Lots of modules that would be useful to a
Heat developer to see documented (e.g. all of heat.common, heat.db) were
not documented, while some other fairly useless ones were.

Change-Id: Ie3aa5bbe8deb8d07eef5fcc352e349a1fa7c68bc

noironetworks/heat,openstack/heat,noironetworks/heat,openstack/heat