automation: include tail of serial log in the gitlab outout

Make it a bit easier to see what has failed.

Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>

automation/scripts/qubes-x86-64.sh

@@ -225,6 +225,9 @@ until grep "^Welcome to Alpine Linux" smoke.serial || [ $timeout -le 0 ]; do
     sleep 1;
     : $((--timeout))
 done
+
+tail -n 100 smoke.serial
+
 if [ $timeout -le 0 ]; then
     echo "ERROR: test timeout, aborting"
     exit 1