Bump src/cloud_controller_ng

Bump cloudfoundry/cloud_controller_ng:
  Michael Fraenkel:
     Fix race condition for creating new users ( Travis started: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/30792827 )
  Matthew Sykes:
     Add instance_memory_limit to quota_definition api, model, controller ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/30776116 )
     Add space quota definition ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/30772517 )
  Julz Friedman:
     Symbolize keys to avoid duplicate fields ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/30753040 )
  Graeme Davison and Joseph Palermo:
     Validate that quota definition memory limit is >= zero. ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/30702399 )
     Add instance_memory_limit to quota definitions ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/30692961 )
  Joseph Palermo:
     Fix test pollution ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/30575189 )

Signed-off-by: Joseph Palermo <jpalermo@pivotallabs.com>