(This is a merge of http://go/wvgerrit/14051)
Adds support for passing a special provisioning response ("delete")
to the provisioning API in order to unprovision the current origin.
Note that the origin MUST be set or else this will fail.
The existing, system-only unprovisionDevice() method is unaffected.
Bug: 12247651
Change-Id: I16d296397d8e9e73c8f43e36c86838873318a398
efea2ddba4