Switch tox unit test command to use ostestr

This commit switches the tox command to use ostestr instead of calling
testr through setup.py. The primary advantage here is that it uses the
subunit-trace output filter. ostestr primarily exists as a replacement for
pretty_tox.sh bash scripts which spread like a plague through OpenStack
projects after Nova copied it from Tempest.

Note that this dramatically increases output while running tests.
However, test failures are still at the bottom of the output, so it
shouldn't cause much pain, if any.

Change-Id: Id1ad26bc9670efa94c3c91142a177c75a12ce7d6

test-requirements.txt

@@ -19,6 +19,7 @@ stevedore>=1.17.1 # Apache-2.0
 testrepository>=0.0.18 # Apache-2.0/BSD
 testresources>=0.2.4 # Apache-2.0/BSD
 testtools>=1.4.0 # MIT
+os-testr>=0.8.0 # Apache-2.0
 python-memcached>=1.56 # PSF
 WebTest>=2.0 # MIT
 

tox.ini

@@ -11,11 +11,12 @@ setenv = VIRTUAL_ENV={envdir}
          CLIENT_NAME=keystonemiddleware
          OS_STDOUT_NOCAPTURE=False
          OS_STDERR_NOCAPTURE=False
+         TESTS_DIR=./keystonemiddleware/tests/unit/
 
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
        .[audit_notifications]
-commands = python setup.py testr --testr-args='{posargs}'
+commands = ostestr {posargs}
 
 [testenv:pep8]
 commands =