Make init handler idempotent.

This fixes the issue when module build is cancelled in init state.

docker/Dockerfile-tests

@@ -43,6 +43,7 @@ RUN yum -y install \
     python-mock \
     python-tox \
     rpm-build \
+    python2-pyyaml \
     && yum clean all
 # We currently require newer versions of these Python packages for the tests.
 # more-itertools is required by pytest, but versions 6.0.0 and up aren't Python 2 compatible