Env cleanup

Created by: bjackman

Some cleanups and simplifications for TestEnv.

Generally:

• Simplify a load of conditionals by
  • Removing the unnecessary case where conf/test_conf is None
  • Using d.get('foo') instead of if 'foo' in d and...
• Use set operations to simplify stuff

I think this also has a sneaky bugfix for installing rt-app dependencies via install_tools but I haven't replicated that presumed bug.