[WFLY-3591] Add keycloak auth to http management endpoint

This PR adds the ability to specify &lt;keycloak/&gt; as the authentication provider for the ManagementRealm in domain-http.  It does not actually pull any Keycloak artifacts into the target build.  On its own, this PR doesn't add any functionality in wildfly-core.  However, this is needed so that Keycloak can be added to wildfly full.
Like I said, it's easy to get this wrong.  :-{

Maybe you can help me.  Does this require I create a brand new jboss-as-config_3_0.xsd file in the server module?   Then I just change the name of the method from parseSecurityRealm_1_4 to parseSecurityRealm_3_0.  Does that sound right?

If so, the method just needs to be called