Close psql processes gracefully in recovery tests
Under windows, psql processes need to be ended explicitly, or the TAP
tests hang. However, the recovery tests were doing this via
IPC::Run::kill_kill(), which causes other major problems on Windows.
We solve this by instead sending '\q' to psql so it quits of its own
accord, and then simply waiting for it. This means we can now run almost
all the recovery tests on all Windows platforms.
Discussion: https://postgr.es/m/
20210301200715.tdjpuesfzebpffgn@alap3.anarazel.de