Make test_host_filters a NoDBTestCase

This is the final patch in the refactoring series. This changes the
test_host_filters.py file to contain just the test of the filter handler
system and cleans up the previously database-creating TestHostFilters
class.

The entire set of host filter unit tests (around 350 of them) now run in
less than 2 seconds, down from over a 45 seconds on my workstation.

Change-Id: I2f2518a08ac3f8c6addcd4055ee4c706c4c92e8e
Move setup_instance_group to conductor

During prework of scheduler split, we identified that
there is a call from setup_instance_group to the Nova object
InstanceGroup. That prevents the scheduler to be split as a
separate project because it would have an external dependency to
a Nova object.
The implementation here is providing the call by the conductor
before the call to select_destinations as this method only
modifies filter_properties for adding group details.

Co-Authored-By: Ed Leafe <ed@leafe.com>

Change-Id: Ib6556c8f6d6e6dcdb65a0bdb1894c66e92b35230
Merge "Move setup_instance_group to conductor"
Merge "Make test_host_filters a NoDBTestCase"