Bump src/etcd-metrics-server

Bump cloudfoundry-incubator/etcd-metrics-server:
  David Varvel:
     fix race condition in test
  phanle:
     Create README.md
  Phan Le:
     Add drone config
     Added dependencies needed for tests
     Added integration test for main
     Move collector registrar to metricz
     Bumped metricz
     More metricz less cfcomponent
     Starting using metricz
     Added metricz
  Alex Suraci:
     Stop using cfcompnent messages
     Use the correct version of component messages