Only do a nova-manage db_sync when we have nova.

- Fixes bug 956226.

Change-Id: I823e8f43425c2d629219bb426fb6aa5d1ab9ff34
diff --git a/stack.sh b/stack.sh
index 5425df9..054b15e 100755
--- a/stack.sh
+++ b/stack.sh
@@ -1359,7 +1359,7 @@
 # All nova components talk to a central database.  We will need to do this step
 # only once for an entire cluster.
 
-if is_service_enabled mysql; then
+if is_service_enabled mysql && is_service_enabled nova; then
     # (re)create nova database
     mysql -u$MYSQL_USER -p$MYSQL_PASSWORD -e 'DROP DATABASE IF EXISTS nova;'
     mysql -u$MYSQL_USER -p$MYSQL_PASSWORD -e 'CREATE DATABASE nova;'