test: Use context system for guest commands

Extends the context system in the test scripts to allow executing commands
within a guest.  Do this without requiring an existing network in the guest
by using socat to run ssh via a vsock connection.

We do need some additional "sleep"s in the tests, because the new
faster dispatch means that sometimes we attempt to connect before
socat has managed to listen.

For now, only use this for the plain "passt" tests.  The "passt_in_ns" and
other tests have additional complications we still need to deal with.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

test/lib/layout

@@ -92,15 +92,13 @@ layout_passt() {
 
 	get_info_cols
 
-	tmux pipe-pane -O -t ${PANE_GUEST} "cat >> ${LOGDIR}/pane_guest.log"
-	tmux select-pane -t ${PANE_GUEST} -T "guest"
-
 	tmux send-keys -l -t ${PANE_INFO} 'while cat /tmp/.passt_test_log_pipe; do :; done'
 	tmux send-keys -t ${PANE_INFO} -N 100 C-m
 	tmux select-pane -t ${PANE_INFO} -T "test log"
 
 	pane_watch_contexts ${PANE_HOST} host host
 	pane_watch_contexts ${PANE_PASST} passt passt
+	pane_watch_contexts ${PANE_GUEST} guest qemu guest
 
 	info_layout "single passt instance with guest"