heat-engine service can be now configured to be either Deployment or
StatefulSet.
Additionally this commit removes /var/cache/heat volume, as it's not
used by heat-engine or other heat services at all.
Change-Id: I541a1efc7817beb5f05d4cce216d9ea1cf378d7a
Co-Authored-By: Mateusz Blaszkowski <mateusz.blaszkowski@intel.com>