v0.57.0-rc1

Release Candidate containing the following features:

• Task Backoff Delay (#3120)
  This feature is opt-in, enable it by adding these lines to your service config.
  Task Backoff Design Document
• Shared Hierarchial Memory Support (#3123)
  This feature is opt-in, enable it by adding shared memory settings to your Service Spec.
  This feature requires SHM support added in Mesos 1.9
  SHM Design Document
• Quota Support (#3102)
  This feature is opt-in, enable it by adding these lines to your service config.
  This config setting will be removed when root Marathon injects this environment-varable with the correct value.
  This feature requires Quota support added in Mesos 1.9
  Quota Design Document
• Batch TaskInfo Writes (#3045)