Add OS_TEST_PATH to testr
Add OS_TEST_PATH to testr

Change default test path to unit tests, and support setting
$OS_TEST_PATH to specify a different path (such as functional).

Change-Id: I237d8c06aaa7912f24b8579cd1b0a72f1517e1b5

openstack/python-muranoclient,openstack/python-muranoclient