add tests for db upgrade with mysql, postgres

test-db-upgrade/docker-db.sh

@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+set -e
+NAME="hub-test-$DB"
+docker rm -f $NAME 2>/dev/null || true
+
+case $DB in
+mysql)
+  ARGS="-p 13306:3306 -e MYSQL_ROOT_PASSWORD=x -e MYSQL_DATABASE=jupyterhub mysql:5.7"
+  ;;
+postgres)
+  ARGS="-p 15432:5432 -e POSTGRES_DB=jupyterhub postgres:9.5"
+  ;;
+*)
+  echo "must be mysql or postgres"
+  exit -1
+esac
+
+set -x
+docker run --rm --name $NAME -d $ARGS