The previous commits improve test failures by dropping relay connections
at shutdown, and flunking a test quickly when one client fails but the
other one hangs.
If that doesn't work (say, some client has a time.sleep(), or other
stall that isn't affected by the relay shutdown), we'll be left with an
active thread holding that hanging client.
This patch adds a check to wormhole.test.common.ServerBase.tearDown that
looks for active threads, waits a second (after stopService), then
checks the threadpool again. If the threadpool is empty, everything is
fine. If not, it prints a message (to stdout) to inform the impatient
user why the test is probably hanging.
This requires a DB delete/recreate when upgrading. It changes the server
protocol, and app IDs, so clients cannot interoperate with each other
across this change, nor with the server. Flag day for everyone!
Now apps do not share channel IDs, so a lot of usage of app1 will not
cause the wormhole codes for app2 to get longer.
