Cirrus-CI: Check for final "Uptime" message

The last thing printed by the kernel after shutdown is Uptime: <time>.
In the CI boot test script add a check for this, to ensure that shutdown
is successful.  A test branch of mine panicked during shutdown, but
still reported success in Cirrus-CI.

Reviewed by:	kevans
Sponsored by:	The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D48823

tools/boot/ci-qemu-test.sh

@@ -125,8 +125,8 @@ timeout 300 \
         -snapshot -hda $hda 2>&1 | tee ${BOOTLOG}
 
 # Check whether we succesfully booted...
-if grep -q 'Hello world.' ${BOOTLOG}; then
-	echo "OK"
+if grep -q 'Hello world.' ${BOOTLOG} && egrep -q '^Uptime: ' ${BOOTLOG}; then
+	echo "Boot successful"
 else
 	die "Did not boot successfully, see ${BOOTLOG}"
 fi