Fix Galera socket for RedHat

At the moment, RedHat currently installs and listens on the
/var/lib/mysql/mysql.sock path, this can be seen by the following:

mysqld  13627 mysql   33u     unix 0xffff88079261cc00        0t0   3312115 /var/lib/mysql/mysql.sock

This patch resolves it which will allow the health checks to
function as they rely on the [client] section which contains
an incorrect path.

Change-Id: Iec88e911c6cf207bcea5bd067f9743b3eb50f60e

vars/redhat-7.yml

@@ -37,7 +37,7 @@ galera_server_required_distro_packages:
 
 galera_etc_conf_file: "/etc/mysql/my.cnf"
 galera_etc_include_dir: "/etc/mysql/conf.d"
-galera_var_run_socket: "/var/run/mysqld/mysqld.sock"
+galera_var_run_socket: "/var/lib/mysql/mysql.sock"
 
 _galera_mariadb_server_package: "MariaDB-server"