bhyve: don't reset domain autostart flag on destroy

bhyve: don't reset domain autostart flag on destroy

Currently, virBhyveProcessStop() uses the virDomainDeleteConfig()
helper to clean up domain status. It passes BHYVE_STATE_DIR as
a configuration dir and NULL as autostart dir, so the helper does its
job, even though it has a different purpose. However, the issue is that
it also resets the autostart (and autostartOnce) property.

This results in a situation that when a persistent domain with autostart
enabled gets destroyed, its autostart state is reported as disabled,
which is not correct.

To fix that, implement the bhyveProcessRemoveDomainStatus() which
removes the status file without side effects on the virDomainObj object.

Signed-off-by: Roman Bogorodskiy <bogorodskiy@gmail.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com