Add support for testrepository

Adds the testrepository config file needed to use testr to run the
tempest tests. To run the tests just do:

testr run

or to run them in parallel:

testr run --parallel

At this stage you may encounter one or two failures with --parallel due to
conflicts between a couple of tests that not have yet been fixed, but a serial
run should work fine.

Change-Id: I08121fdcd48e2f4ff86bf9e1d4d378f818699d89