Setting Maven Mirror URL does not exclude Decision Central

If a user specifies a maven mirror url in the templates, then that mirror should exclude Decision Central in it's "mirror of" config. Otherwise, maven in the KIE Server will attempt to look to Decision Central for external artifacts.

To fix this, the following should be added to the deployment config for all kie servers (note that only the authoring templates will also include its exclusion by default):

          - name: MAVEN_MIRROR_OF 
            value: "external:*,!${APPLICATION_NAME}-rhdmcentr" 
          - name: RHDMCENTR_MAVEN_REPO_ID 
            value: "${APPLICATION_NAME}-rhdmcentr"

The above only takes affect if a MAVEN_MIRROR_URL is specified, so this will not affect current behavior otherwise.