wait_for_ssh counted only its sleeps toward the timeout. Under QEMU user
networking each attempt can also spend its whole ConnectTimeout waiting
for a banner, so a "300 s" wait ran for ten minutes or more without a
line of output. It now uses a wall-clock deadline, polls every 2 s, and
prints a progress line with a console screenshot every 30 s. When the
boot scenario times out it prints the serial console's last lines too.
Emir Beganovic
84149ef33b