Using python to run testr instead

So tox will not report bash is not installed in testenv.

Fixes bug #1233024

Change-Id: Ifed717df51340b2834f2f0522125a842495dcdda

tox.ini

@@ -7,8 +7,7 @@ setenv = LANG=en_US.UTF-8
          LC_ALL=C
 deps= -r{toxinidir}/test-requirements.txt
 commands=
-    bash -c 'if [ ! -d ./.testrepository ] ; then testr init ; fi'
-    bash -c 'testr run --parallel {posargs} ; RET=$?; echo "Slowest Tests" ; testr slowest && exit $RET'
+    python setup.py testr --slowest --testr-args='{posargs}'
 
 [testenv:pep8]
 commands =