WFLY-2171 Use deployment unit processors to register mod_cluster metrics

Hopefully last version of  https://github.com/wildfly/wildfly/pull/5573 and https://github.com/wildfly/wildfly/pull/5164 using the original approach.

Jira:
https://issues.jboss.org/browse/WFLY-2171

Metrics are now installed for enabled/configured metrics and thus minimazing the overheard for them to work.