Promisify modules (#6723)

* WIP promisify

* promisify psql

* ability to skip some keys

* dont promisify client object

* remove async

* clone entire module so it has all properties

* add shim for node 6

* ignore sessionStore as well

* ignore pool on psql

src/promisify.js

@@ -0,0 +1,37 @@
+'use strict';
+
+// remove once node 6 support is removed
+require('util.promisify/shim')();
+
+var util = require('util');
+var _ = require('lodash');
+
+module.exports = function (theModule, ignoreKeys) {
+	ignoreKeys = ignoreKeys || [];
+	function isCallbackedFunction(func) {
+		if (typeof func !== 'function') {
+			return false;
+		}
+		var str = func.toString().split('\n')[0];
+		return str.includes('callback)');
+	}
+	function promisifyRecursive(module) {
+		if (!module) {
+			return;
+		}
+		var keys = Object.keys(module);
+		keys.forEach(function (key) {
+			if (ignoreKeys.includes(key)) {
+				return;
+			}
+			if (isCallbackedFunction(module[key])) {
+				module[key] = util.promisify(module[key]);
+			} else if (typeof module[key] === 'object') {
+				promisifyRecursive(module[key]);
+			}
+		});
+	}
+	const asyncModule = _.cloneDeep(theModule);
+	promisifyRecursive(asyncModule);
+	return asyncModule;
+};