Bump src/cloud_controller_ng

Bump cloudfoundry/cloud_controller_ng:
  Kai Zhang:
     Add unit tests for Drain class in lib/cloud_controller ( Travis Unknown )
  Abhijit Hiremagalur:
     Extract logic from drain hook to bring it under test ( Travis Unknown )

Signed-off-by: Matthew Sykes <matthew.sykes@gmail.com>