Edits assert methods

Makes changes to 3 files:
tests/network/services/test_fwaas.py
tests/network/services/test_lbaas.py
tests/network/services/test_vpnaas.py

Replaces assertTrue(a not in b) with assertNotIn(a, b),
and assertTrue(a in b) with assertIn(a, b).

Change-Id: I01e683569d9b8116f2dbadbf8fe4cb0024625178
Merge "Edits assert methods"