incompatible changes:
- Add GetDevicePluginOptions rpc call. This is needed when we switch
  from Registration service to probe-based plugin watcher.
- Change AllocateRequest and AllocateResponse to allow device requests
  from multiple containers in a pod. Currently only made mechanical
  change on the devicemanager and test code to cope with the API but
  still issues an Allocate call per container. We can modify the
  devicemanager in 1.11 to issue a single Allocate call per pod.
  The change will also facilitate incremental API change to communicate
  pod level information through Allocate rpc if there is such future
  need.