r315112:
Add the capability to refresh the gpart(8) label without need a reboot.
gpart(8) has functionality to change the label of an GPT partition.
This functionality works like it should, however, after a label change
the /dev/gpt/ entries remain unchanged. glabel(8) status output remains
unchanged. The change only takes effect after a reboot.
r315196:
After r315112 I broke the tests with eli, instead to pass 0, I should pass
M_NOWAIT to g_media_changed() that will call g_post_event() with this flag.