Remove intermediate qubesd-query-fast proxy process.
This requires changing socket protocol to match what qrexec is sending
in the header.
FixesQubesOS/qubes-issues#3293
Add few missing app.close() calls on test teardown.
Fix socket cleanup in TC_00_QubesDaemonProtocol() - not only close the
FD, but also unregister it from asyncio event loop.
Recently libvirt removed support for changing event implementation.
Therefore we have to use a single, global one and we check if it is
empty between tests.
