Add maximum time-out to sync operation

BUG: 16219182
We have seen cases where run-away syncs keep going for a very long time.
The default behaviour is that a sync can run for as long as it wants once
there is nothing else waiting.
This CL will change that, and impose a maximum time-limit of 30mins on
each sync, after when the op with be cancelled and the adapter will go
into back-off.
This behaviour will only take effect for syncs that are not initializations,
or user-initiated.

Change-Id: I1731270ca2a6500b19fc125186aa0b0cd81d1126