Add run_test.sh for running tests

This is a copy of the test entry point used in Nova, Swift, Keystone,
Tuskar, Glance, Horizon, Neutron, Heat, Cinder, and others. It
provides a simple way to add consistency and repeatability to running
tests w/ minimal human effort, just run ./run_tests.sh.

Change-Id: I5469cdeacb933d30868596e5bb9e767b17ab44d2