Fix /usr/local/bin/matrix-dendrite-create-account

We also need to fix `--tags=register-user`. This tag is currently
defined in both the `matrix-synapse` and `matrix-dendrite` roles.

roles/matrix-dendrite/templates/dendrite/usr-local-bin/matrix-dendrite-create-account.j2

@@ -9,4 +9,4 @@ fi
 user=$1
 password=$2
 
-docker exec matrix-dendrite create-account --config /data/dendrite.yaml --user "$user" --password "$password"
+docker exec matrix-dendrite create-account -config /data/dendrite.yaml -username "$user" -password "$password"