Replace EMS_IDs with EMS_ID in container entrypoint

Workers having a comma separated list of EMS IDs is no longer used and
this can be simplified to a single EMS_ID.

images/manageiq-base-worker/container-assets/entrypoint

@@ -3,7 +3,7 @@
 [[ -s ${APP_ROOT}/container_env ]] && source ${APP_ROOT}/container_env
 
 WORKER_OPTIONS=""
-[[ -n $EMS_IDS ]] && WORKER_OPTIONS="${WORKER_OPTIONS} --ems-id=${EMS_IDS} "
+[[ -n $EMS_ID ]] && WORKER_OPTIONS="${WORKER_OPTIONS} --ems-id=${EMS_ID} "
 [[ -n $HOSTNAME ]] && WORKER_OPTIONS="${WORKER_OPTIONS} --system-uid=$HOSTNAME "
 
 exec ruby ${APP_ROOT}/lib/workers/bin/run_single_worker.rb --heartbeat ${WORKER_OPTIONS}${WORKER_CLASS_NAME}