bhyve: restore persistent definition after process stop

bhyve: restore persistent definition after process stop

The virBhyveProcessStop() function which handles bhyve process
shutdown does not remove the transient definition, meaning
that it overrides the persistent definition.

Update it to call virDomainObjRemoveTransientDef(). Also, move the body
of the code to virBhyveProcessStopImpl() which accepts 'restoreDef'
argument telling whether the transient definition should be removed.

That is necessary as reboot is implemented as stop + start, and
in this case the transient definition should not be removed.

Closes: https://gitlab.com/libvirt/libvirt/-/work_items/900
Signed-off-by: Roman Bogorodskiy <bogorodskiy@gmail.com>
Reviewed-by: Martin Kletzander <mkletzan@redhat.com>