Use subunit colorizer from nova for run_tests.sh

This commit copies the colorizer.py script over from nova and enables
it for testr with run_tests.sh. This enables real time output from
testr about which tests ran and the result with colors.

Change-Id: Idd1b820d103bf4d71f2645e98e86e5fadbd6cb0c
Merge "Use subunit colorizer from nova for run_tests.sh"