H2O: Use 2 database connections per thread (#7717)

frameworks/C/h2o/h2o.sh

@@ -27,7 +27,7 @@ fi
 if [[ "$BENCHMARK_ENV" = "Azure" ]]; then
 	DB_CONN=2
 else
-	DB_CONN=1
+	DB_CONN=2
 fi
 
 build_h2o_app()