add metric-registrar plugin
add metric-registrar plugin

Signed-off-by: Peter Stone <ed3c959c69b6cb387f8019221bf033c27f28453c@pivotal.io>

cloudfoundry-incubator/cli-plugin-repo,cloudfoundry-incubator/cli-plugin-repo,kkellner/cli-plugin-repo,cloudfoundry-incubator/cli-plugin-repo,cloudfoundry-incubator/cli-plugin-repo,kkellner/cli-plugin-repo,kkellner/cli-plugin-repo