Intermittent test failure

[stuarteberg]

The test that verifies parallel read and write access fails intermittently, as if the server needs more time to initialize, even though that makes no sense. I can't come up with any explanation for the specific error that occurs. For now, I've inserted a delay into the test. It would be nice to understand this failure.

FWIW, this is the exception that pops up in the server:

Traceback (most recent call last):
  File ".../DVIDResourceManager/dvid_resource_manager/server.py", line 254, in <module>
    sys.exit( main() )
  File ".../DVIDResourceManager/dvid_resource_manager/server.py", line 79, in main
    server.run(args.debug)
  File ".../DVIDResourceManager/dvid_resource_manager/server.py", line 168, in run
    self.finish_work(request["id"])
  File ".../DVIDResourceManager/dvid_resource_manager/server.py", line 241, in finish_work
    request = self.current_work_items[curr_id]
KeyError: 0