VM hard_shutdown and hard_reboot should wait for nothing else.

VM hard_shutdown and hard_reboot should wait for nothing else.

We were already allowing hard_reboot concurrent with a clean_reboot
already in progress, and the same for hard/clean shutdown, but
clean_(shutdown|reboot) would block hard_(reboot|shutdown).

Now the is_allowed_concurrently function allows hard_shutdown
concurrent with anything except itself, and allows hard_reboot
concurrent with anything but itself or hard_shutdown.

CA-139501