torture: Make kvm-test-1-run-qemu.sh check for reboot loops

It turns out that certain types of early boot bugs can result in reboot
loops, even within a guest OS running under qemu/KVM.  This commit
therefore upgrades the kvm-test-1-run-qemu.sh script's hang-detection
heuristics to detect such situations and to terminate the run when
they occur.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>