ci: don't hang on kernel crashes in qemu

Backport of kernel-patches PR ([0]), done by @thefallentree.

  [0] https://github.com/kernel-patches/vmtest/pull/29

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

travis-ci/vmtest/run.sh

@@ -459,10 +459,10 @@ if kvm-ok ; then
 else
   accel="-cpu qemu64 -machine accel=tcg"
 fi
-qemu-system-x86_64 -nodefaults -display none -serial mon:stdio \
+qemu-system-x86_64 -nodefaults -display none -serial mon:stdio -no-reboot \
   ${accel} -smp "$(nproc)" -m 4G \
   -drive file="$IMG",format=raw,index=1,media=disk,if=virtio,cache=none \
-  -kernel "$vmlinuz" -append "root=/dev/vda rw console=ttyS0,115200$APPEND"
+  -kernel "$vmlinuz" -append "root=/dev/vda rw console=ttyS0,115200 kernel.panic=-1 $APPEND"
 sudo mount -o loop "$IMG" "$mnt"
 if exitstatus="$(cat "$mnt/exitstatus" 2>/dev/null)"; then
 	printf '\nTests exit status: %s\n' "$exitstatus" >&2