Move the full-balance warning to before the fork, so that the user can
see and react to it.
Notes on test:
- Don't use grep -q, as it causes a SIGPIPE during the countdown, and
the balance thus doesn't start.
- The "balance cancel" is superfluous as the last command, but it
provides some idempotence and allows adding more tests below it.
Issue: #168
Signed-off-by: Vladimir Panteleev <git@vladimir.panteleev.md>
Signed-off-by: David Sterba <dsterba@suse.com>