MDEV-7319 : Galera bootstrap (/etc/init.d/mysql bootstrap)

            returns code 0 on failure

Modified init script to return with proper exit status for
bootstrap command. [Based on Kenny Rasschaert's suggestion]

support-files/mysql.server.sh

@@ -445,8 +445,9 @@ case "$mode" in
   'bootstrap')
       # Bootstrap the cluster, start the first node
       # that initiate the cluster
-      echo $echo_n "Bootstrapping the cluster"
+      echo $echo_n "Bootstrapping the cluster.. "
       $0 start $other_args --wsrep-new-cluster
+      exit $?
       ;;
   *)
       # usage