Actually recognize the kill_parent_process recovery rule and invoke the
kernel module correctly.

Changes to make startup of process work (more) correctly. Argument parsing
was mishandled in some cases. Start all commands via "sh -c" so that there
is a "regular" parent process to kill with future kill_parent_process
invocations. Otherwise, we would kill the kernel user-mode helper thread.

Make sure we don't ever try to kill process 1 (which can happen for a
detached process that triggers the kill_parent rules). Otherwise, the
party ends rather abruptly.

Get rid of all the "exit(0)" calls within functions called when taking
a snapshot, just return an error so that we can retry the snapshot (after
letting the guest run briefly). This required further memory cleanup
code in a (large) number of places. These inconsistent snapshots seem
to happen quite a lot when running at high frequency and when the guest
is busy.