Make database.initialize async

src/database.js

@@ -32,10 +32,8 @@ const gDatabase = {
     name: 'box'
 };
 
-function initialize(callback) {
-    assert.strictEqual(typeof callback, 'function');
-
-    if (gConnectionPool !== null) return callback(null);
+async function initialize() {
+    if (gConnectionPool !== null) return;
 
     if (constants.TEST) {
         // see setupTest script how the mysql-server is run
@@ -66,14 +64,12 @@ function initialize(callback) {
         connection.query('USE ' + gDatabase.name);
         connection.query('SET SESSION sql_mode = \'strict_all_tables\'');
     });
-
-    callback(null);
 }
 
-function uninitialize(callback) {
-    if (!gConnectionPool) return callback(null);
+async function uninitialize() {
+    if (!gConnectionPool) return;
 
-    gConnectionPool.end(callback);
+    gConnectionPool.end();
     gConnectionPool = null;
 }