Enable ResourceUnknownStatus to report status_reason

This patch enables the ResourceUnknownStatus exception to report the
detailed resource status reason (if given).  By default, the status
reason is set to 'Unknown'.

Change-Id: I9b9d1ebdb1cd16be5bf0a82567aef18537e9d52c
Closes-Bug: 1401522
Merge "Enable ResourceUnknownStatus to report status_reason"