set private_ip variable (proxy fun)

Author: glasnt

cloud-sql/sqlserver/tedious/ci-setup.json

@@ -6,7 +6,8 @@
       "CLOUD_SQL_CONNECTION_NAME": "$INSTANCE_CONNECTION_NAME",
       "INSTANCE_UNIX_SOCKET": "$UNIX_SOCKET_DIR/$INSTANCE_CONNECTION_NAME",
       "DB_NAME": "kokoro_ci",
-      "DB_USER": "kokoro_ci"
+      "DB_USER": "kokoro_ci",
+      "PRIVATE_IP": "1"
     },
     "secrets": {
       "DB_PASS": "nodejs-docs-samples-tests/nodejs-docs-samples-sql-password"