Improve error message on connector init error

[Back-port pull request #859]

lib/datasource.js

@@ -327,6 +327,7 @@ DataSource.prototype.setup = function (name, settings) {
 
     }.bind(this);
 
+    try {
       if ('function' === typeof connector.initialize) {
         // Call the async initialize method
         connector.initialize(this, postInit);
@@ -335,6 +336,14 @@ DataSource.prototype.setup = function (name, settings) {
         this.connector = new connector(this.settings);
         postInit();
       }
+    } catch(err) {
+      if (err.message) {
+        err.message = 'Cannot initialize connector ' +
+          JSON.stringify(connector.name || name)  + ': ' +
+          err.message;
+      }
+      throw err;
+    }
   }
 
   dataSource.connect = function (cb) {