set dbc_dbuser in postinst too

debian/postinst

@@ -315,7 +315,12 @@ case "$1" in
         echo "Reloading nginx configuration..."
         invoke-rc.d nginx reload
       fi
-    dbc_go $gitlab_user "$@"
+    
+    dbc_dbtypes="pgsql"
+    dbc_dbname="gitlab_production"
+    dbc_dbuser="$gitlab_user"
+
+    dbc_go gitlab "$@"
     db_stop
 
     # enable the pg_trgm extension