Rename the remaining instance group tests for clarity

In preparation to move these tests to functional tests rename and
document what they do.
This also simplifies the launch config test as it does not need
the scaling group for this test.

Part of blueprint decouple-nested
Change-Id: I77d7fb38b852590a3004532d28b9b9fcf29dc819
Merge "Rename the remaining instance group tests for clarity"