Make run_tests.sh for running unit tests

In other projects the run_tests.sh script is used for project
verification (ie running unit tests) However, because tempest didn't
have unit tests and is itself a test suite the run_tests.sh script was
used to execute the tempest tests. Now that we have unit tests starting
to trickle into tempest the run_tests.sh script can be used for it's
traditional purpose. So, this commit removes the tempest specific
functionality from run_tests.sh and makes it run the unit tests.

Partially implements bp unit-tests

Change-Id: Iac4e9d0908274a20c3d278b2c8d7e00949a1f36e
Merge "Make run_tests.sh for running unit tests"