Add test coverage for bug 1943724

Now that bug 1943724 is fixed in neutron we can extend the tempest test
coverage to show that changing the direction of the QoS minimum
guaranteed bandwidth rule on a bound port is supported.

Related-Bug: #1943724

Change-Id: I09e773baedcffc8af5a88e0be1df38d14633ed74
1 file changed