app: Fix "Failed to open sql connection" error

The app should wait for a moment even after TCP connection to the
database is available.

Rollback a part of ac0b706.

app/docker-entry.sh

@@ -10,13 +10,15 @@ else
     echo SKIP
 fi
 
-# Wait to avoid "panic: Failed to open sql connection pq: the database system is starting up"
 echo "Wait until database is ready..."
 until nc -z db $DB_PORT_5432_TCP_PORT
 do
     sleep 1
 done
 
+# Wait to avoid "panic: Failed to open sql connection pq: the database system is starting up"
+sleep 1
+
 echo "Starting platform"
 cd /mattermost/bin
 ./platform