MEDIUM: systemd: be more verbose about the reload

MEDIUM: systemd: be more verbose about the reload

When the `haproxy -c` check during the reload fails, no error is output
in the logs, this can be quite bothersome to understand what's going on.

This patch removes the -q option on the check so we can see the error
with `journalctl -u haproxy` or `systemctl status haproxy`

This will change the behavior when the check works, and will display
"Configuration file is valid"

Note that in some case this test could be completely removed, because
the master process loads the configuration itself and is able to keep
the previous workers running when the reload failed. This is interesting
to disable the test when there are a lot of certificates of files to
load, to divide the reload time by 2.

No need to backport.