Use ostestr for running unit tests

This commit switches the test runner to be ostest in the tox.init.
This will ensure that the output formatting of subunit2sql is inline
with other projects.

Change-Id: I4fc0eeb6678c1fa6e2625bf8f81eef0faf77d3a7

test-requirements.txt

@@ -10,3 +10,4 @@ testtools>=0.9.34
 oslosphinx
 MySQL-python
 psycopg2
+os-testr

tox.ini

@@ -10,7 +10,7 @@ setenv = VIRTUAL_ENV={envdir}
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
 commands =
-    python setup.py test --slowest --testr-args='{posargs}'
+    ostestr {posargs}
 
 [testenv:pep8]
 sitepackages = False