Paralleize quantum unit testing:

This change switches run_tests.sh to use testr
in parallel mode, instead of nosetests, in order
to enable unit tests to run in parallel.

By default, the number of parallel test processes
is set to the number of cores on the test machine.

A similar change was recently merged to nova:
  https://review.openstack.org/#/c/15078/

Some tests required updating to remove inter-testcase
dependencies.

bug #1099694

Change-Id: Idfb923d424342a07dcba88d70b971683f549f763