libvirt_lxc: Claim success for --help

So far, if libvirt_lxc binary (usually to be found under
/usr/libexec/) is run with --help, due to a missing line
and our usual functions pattern, an 'uknown' error is returned.
Yeah, the help is printed out, but we should not claim error.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
(cherry picked from commit fb0ef0d5110dd737bde2b79e17c12b71a69f5d06)

src/lxc/lxc_controller.c

@@ -2571,6 +2571,7 @@ int main(int argc, char *argv[])
             fprintf(stderr, "  -S NAME, --security NAME\n");
             fprintf(stderr, "  -h, --help\n");
             fprintf(stderr, "\n");
+            rc = 0;
             goto cleanup;
         }
     }