devstack: Fix redis install when coordination URL uses redis

_ceilometer_prepare_coordination() installs redis when the coordination
backend is redis, but the condition referenced CEILOMETER_COORDINATOR_URL
(a non-existent variable) instead of CEILOMETER_COORDINATION_URL. The
check therefore never matched and redis was not installed.

This was previously masked because CEILOMETER_CACHE_BACKEND also triggered
redis installation. After switching to the global CACHE_BACKEND in
cfe9c0fc5, the redis installation was not done even though
CEILOMETER_COORDINATION_URL defaults to redis://localhost:6379.

Change-Id: I9f767274e28fbe70e2877aa5949ffea125a9e67e
Co-Authored-By: Jaromir Wysoglad <jwysogla@redhat.com>
Signed-off-by: Daniel Pawlik <dpawlik@redhat.com>

devstack/plugin.sh

@@ -81,7 +81,7 @@ function _ceilometer_install_redis {
 function _ceilometer_prepare_coordination {
     if echo $CEILOMETER_COORDINATION_URL | grep -q '^memcached:'; then
         install_package memcached
-    elif [[ "${CEILOMETER_COORDINATOR_URL%%:*}" == "redis" || "${CEILOMETER_CACHE_BACKEND##*.}" == "redis" || "${CEILOMETER_BACKENDS}" =~ "gnocchi" ]]; then
+    elif [[ "${CEILOMETER_COORDINATION_URL%%:*}" == "redis" || "${CACHE_BACKEND##*.}" == "redis" || "${CEILOMETER_BACKENDS}" =~ "gnocchi" ]]; then
         _ceilometer_install_redis
     fi
 }