Split out metrics filter unit tests

Breaks out the metrics filter unit tests from test_host_filters.py

Change-Id: I6b170c3bdc0b91b8b1d590a404db5cb3f460e6a8
Move group affinity filters tests to own test file

The group affinity filter unit tests remained in the
test_host_filters.py test file. We simply move them to
test_affinity_filters.py in this patch.

Change-Id: Ic10a5ba2875de42f1f83d30e6d9bd982dffc17e4
Merge "Split out metrics filter unit tests"
Merge "Move group affinity filters tests to own test file"