Automatic merge from submit-queue

Allow handlers earlier in a request flow to inject a UID for an object

This lets admission controllers specify a stable UID for an object prior to its creation.  That lets the admission controller then record a reference to the object on another resource using that stable UID prior to the object being created.  This would be a prerequisite for supporting quota reservations.

/cc @smarterclayton @lavalamp @deads2k