Run testr init if required

heat-templates gate jobs are currently failing due to lack of
.testrepository.

Change-Id: Ia3b487f8634b9382a42b46ad4bf137dafd96277a

tox.ini

@@ -7,7 +7,8 @@ skipsdist = True
 setenv = VIRTUAL_ENV={envdir}
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
-commands = testr run {posargs}
+commands = bash -c 'if [ ! -d ./.testrepository ] ; then testr init ; fi'
+           testr run {posargs}
 
 [testenv:pep8]
 commands = flake8