If we handle the flux errors in the query controller, it makes it so we
are handling the errors in the location where the happen rather than at
a layer further up the stack.
This should simplify it so the errors are handled in this single
location instead.
In the QueueSize test, it was possible that after the `done` channel was
closed, one of the queries from the queue would begin executing. If all
three began executing before the shutdown was done, the third would
block on attempting to send a value to the `executing` channel and it
would never finish so the controller would report that shutdown failed.
This increases the queue size to a combination of the concurrency quota
and the queue size so all of the started queries will never block when
sending a signal to the executing channel.
The controller implementation is primarily used by influxdb so it
shouldn't be part of the flux repository. This copies the code from flux
to influxdb so it can be removed from the next flux release.
Jonathan A. Sternberg
Christopher Wolff