Merge pull request
#2808 from minrk/parallel_wait...
Merge pull request
#2808 from minrk/parallel_wait
improve patience for slow Hub in client tests
adds a first step in `_wait_for_idle`, where it waits for all tasks to arrive before waiting for no tasks to be running. On a super slow machine, it was possible for `_wait_for_idle` to return prematurely, before tasks had even started.
closes
#2807