virttest.qemu_virtio_port: Log the GW output on failure

Log the output on failure after read-out too.

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
qemu.tests.virtio_console: Check for new data in loopback test

Thread might be alive, but hung on data recv/send. With this check
the test is interrupted after 1s of inactivity. It doesn't check for
new data on the sender thread as with some settings (big send buffer
and small recv buffers) the queue might be filled and this thread
has to wait for new data. This is expected behaviour.

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
qemu.tests.virtio_console: Fix incorrect variable name and style

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
virttest.qemu_virtio_port: Modify GuestWorker cleanup to suit windows

Windows doesn't have killall command and the worker is killed by the
missing connection anyway.

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>