Allowing override to wsrep_on

Adding wsrep_on override to my.cnf

galera/files/my.cnf

 innodb_doublewrite=0
 innodb_autoinc_lock_mode=2
 innodb_locks_unsafe_for_binlog=1
+{%- if service.get('wsrep_enabled', False) %}
+wsrep_on=OFF
+{%- else %}
 wsrep_on=ON
+{%- endif %}
 {%- if service.get('members', []) |length > 1 %}
 wsrep_cluster_address="gcomm://{% for member in service.members %}{{ member.host}}:4567{% if not loop.last %},{% endif %}{% endfor %}/?pc.wait_prim=no"
 {%- else %}