engine: fix 2 findbugs errors

Mistakenly merged while introducing cluster policy feature:
1) new unused variable in ClusterModel.
2) referencing an object prior a nullity check.

Signed-off-by: Gilad Chaplik <gchaplik@redhat.com>
Change-Id: I7c83849a810e398b70c2488ab8a9fd2550e4ce17