Merge pull request kubernetes#1168 from msau42/storage-topology-design

Automatic merge from submit-queue.

Add more details to volume scheduling design

Done:
* Added diagram showing new additions to the scheduler flow
* Restrict new behavior through StorageClass API to eliminate backwards compatibility issues and no need for deprecation.
    * This also eliminates the requirement to support scheduler bypass use cases.
* Caching overview
* Handling other volume predicates correctly

@kubernetes/sig-storage-proposals 
@kubernetes/sig-scheduling-proposals