Implemented missing OStoreDB::RetrieveJob::fail()

The retrieve request now gets properly queued in case of retrieve error.
The errors are counted and the request gets deleted eventually.
A new field was added to the retrive request in object store. This commit
will fail on upgrade if there are retrieve requests still queued at update time.
Cleaned up some unused structures in cta.proto
Minor modifications to ArchiveJobs.