Add a timeout deferred function
Time out the verified_delete call
Pass the LoopingCall's clock to timeout_deferred
Fix some docstrings
Also times out the worker, since thats small.  Fixes AUTO-465
Clarify docstring about the timeout method helper tests
Timeout helper should not return the same deferred it was passed
Timeout helper test case name and docstring changes
Fix the clock advancing test in timer helper
Pass a function to the deferred __init__ that logs when cancelled
Describe the mechanism of timeout in more detail
Implement verified delete using timeout_deferred and retry
change wait_for_active to use retry and timeout_deferred
Refactor worker to use the new retry stuff