Start MySQL on localhost for galera_secure_node

When running MySQL on bare metal, it starts up the secure script
before configuring anything which means that it listens on all
interfaces by default.

In scenarios where the load balancer might be colocated with the
database server, it would cause a conflict and it would refuse
to start up (even if the database server is already configured
not to listen on that interface, the configuration only gets
dropped later in the play).

This sets the environment configuration to start it up on localhost
only and then resets it once it is done.  It should not affect
existing deployment but help with bare metal ones.

Change-Id: I883e32678ea3cc2eea09d23db5eecfce35aee6f2

templates/galera_secure_node.j2

@@ -19,6 +19,7 @@ STOP_MYSQL=false
 
 if ! systemctl status mysql; then
   STOP_MYSQL=true
+  systemctl set-environment MYSQLD_OPTS="--bind-address=127.0.0.1"
   systemctl start mysql
   sleep 10
   systemctl status mysql
@@ -41,4 +42,5 @@ if [ "${STOP_MYSQL}" = true ]; then
 fi
 
 # Create a marker file to ensure this script is not run again
+systemctl unset-environment MYSQLD_OPTS
 touch "/var/lib/mysql/osa_default_secured"