Move test_default_limits to the new tests location

This test apparently landed in the wrong package after the tests well
re-factored. Moving it to the right location.

Implements blueprint refactor-system-tests

Change-Id: I4d01772afce669f42e4d4693ff72d55bea5438ef
Require oslo.config 1.2.0 final

Now that 1.2.0 has been released, require it rather than one of the beta
release tarballs.

Closes-Bug: #1182861
Change-Id: I75ffc4a572d14488d19491a38742d6920951c171