Bump src/cloud_controller_ng

Bump cloudfoundry/cloud_controller_ng:
  Abhijit Hiremagalur:
     Reduce knowledge about the db in positioner ( Travis started: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/22055319 )
     Encapsulate shift_to_position in update ( Travis Unknown )
     Extract BuildpackPositioner ( Travis Unknown )
     Need to call destroy to exercise after_destroy ( Travis Unknown )
     Remove dead code related to prioritized buildpacks ( Travis Unknown )