docker: Fix duplicate "hostname" configuration entry

When the chasquid docker container is restarted, entrypoint.sh will add
the hostname again, even if it is present.

This causes chasquid to fail to start due to the duplicated option
(`non-repeated field "hostname" is repeated`).

Thanks to Jaywann@github for finding and reporting this problem, on
https://github.com/albertito/chasquid/issues/16.

This patch fixes the issue by only adding the option if it isn't already
present.

docker/add-user.sh

@@ -30,6 +30,7 @@ ENCPASS=$(doveadm pw -u "${EMAIL}" -p "${PASSWORD}")
 
 # Edit dovecot users: remove user if it exits.
 mkdir -p /data/dovecot
+touch /data/dovecot/users
 if grep -q "^${EMAIL}:" /data/dovecot/users; then
 	cp /data/dovecot/users /data/dovecot/users.old
 	cat /data/dovecot/users.old | grep -v "^${EMAIL}:" \

docker/entrypoint.sh

@@ -95,8 +95,9 @@ done >> /etc/dovecot/auto-ssl.conf
 # Pick the default domain as default hostname for chasquid. This is only used
 # in plain text sessions and on very rare cases, and it's mostly for aesthetic
 # purposes.
-echo "hostname: '$ONE_DOMAIN'" >> /etc/chasquid/chasquid.conf
-
+if ! grep -iq "hostname:" /etc/chasquid/chasquid.conf; then
+	echo "hostname: '$ONE_DOMAIN'" >> /etc/chasquid/chasquid.conf
+fi
 
 # Start the services: dovecot in background, chasquid in foreground.
 start-stop-daemon --start --quiet --pidfile /run/dovecot.pid \