Bump src/cloud_controller_ng

Bump cloudfoundry/cloud_controller_ng:
  Chris Adams:
     Merge pull request #188 from fraenkel/addbuildpacks ( Travis started: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/22044518 )
  Ruth Byers:
     On drain, unregister from the router and wait before shutting down ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/21981348 )
  fraenkel:
     Use the new buildpack installer task ( Travis Unknown )

Signed-off-by: Kai Zhang <kaizhang@cn.ibm.com>