Raise mysql start timeout to fix deploy on slow platforms

Change-Id: Ic8a55debf90d47c33cc0b6f0b9d8501b5d48f9c6
diff --git a/docker/swarm/stack/gerrit.yml b/docker/swarm/stack/gerrit.yml
index 98222fc..48466ef 100644
--- a/docker/swarm/stack/gerrit.yml
+++ b/docker/swarm/stack/gerrit.yml
@@ -50,6 +50,7 @@
                 MYSQL_PASSWORD: ${_param:mysql_gerrit_password}
                 MYSQL_DATABASE: gerrit
                 MYSQL_ROOT_PASSWORD: ${_param:mysql_admin_password}
+                MYSQL_START_TIMEOUT: 300
               deploy:
                 restart_policy:
                   condition: any