Remove unused jenkins arguments from tox.ini

These do not match the established testing patterns for OpenStack and
seem to be quite redundant. They also mention nosetests which is no
longer used.

Change-Id: I874a226b515f1a8ad24136eba81a40fc170435b9
Fix test_dbinstance not running by itself

This test seems to need a clean copy of the db like many others. Call
setup_dummy_db to initialize so it runs reliably by itself.

Change-Id: I60fcd6b5c94659f16ef85ca3bdbd61417c59322b
Refactor instance tests to share common code

Change-Id: I565f6aee43d07f3fc451538ca02f9398eedebaf3
Merge "Refactor instance tests to share common code"
Merge "Remove unused jenkins arguments from tox.ini"
Merge "Fix test_dbinstance not running by itself"