Add nosehtmloutput as a test dependency.

Backported from https://review.openstack.org/11759

Adding nosehtmloutput as a test dependency allows nose to output its
results to an html file. This will be used by Jenkins to save logs
on a different server.

This also enables the run-tox.sh check for "Ran 0 tests" false
positives.

Change-Id: Ia9ed0527dc234fb6c744d0a0a700ba5edb3f7088