...if the restoring data engine thread winds up operations. By closing
the engine side of the pipe unconditionally when exiting the thread,
the unanticipated-failure path is now guaranteed (instead of blocking
forever in write() to a pipe that isn't being read!).
In addition, wire agent-timeout handling into the various stream
data-handling operations (preflight, backup, restore). This were
not sufficiently robust and were in some situations leaving the
backup/restore mechanisms in a livelock state.
Finally, plug a longstanding problem in which we'd have orphaned
timeout messages coming in and producing a certain amount of "wtf?"
logging and wasted CPU. No longer!
Bug 28457158
Change-Id: I597c76c3eada378ffeb20870253847594f73e089
35c2827c60