[type/__sshd_config] Produce error if invalid config file is generated

Previously, cdist would silently swallow the error (no invalid config file was
generated).

Reason: `set -e` does not exit if a command in a sub-command group fails,
it merely returns with a non-zero exit status.

e.g. the following snippet does not abort the script if sshd -t returns with a
non-zero exit status:

    set -e
    cmp -s old new || {
        # check config file and update it
        sshd -t -f new \
        && cat new >old
    }

or compressed:

    set -e
    false || { false && true; }
    echo $?
    # prints 1

cdist/conf/type/__sshd_config/gencode-remote

@@ -91,7 +91,8 @@ awk $(drop_awk_comments "${__type:?}/files/update_sshd_config.awk") \\
 
 cmp -s $(quote "${sshd_config_file}") $(quote "${sshd_config_file}.tmp") || {
 	sshd -t -f $(quote "${sshd_config_file}.tmp") \\
-	&& cat $(quote "${sshd_config_file}.tmp") >$(quote "${sshd_config_file}")
+	&& cat $(quote "${sshd_config_file}.tmp") >$(quote "${sshd_config_file}") \\
+	|| exit  # stop if sshd_config file check fails
 }
 rm -f $(quote "${sshd_config_file}.tmp")
 EOF