moduleFor could accept callback as second argument

[ppcano]

This function argument contract are closed to the qunit module API.

In much of the cases, developers would write integration tests through qunit module and unit tests with ember-qunit module api, in that case, having the module method to support the same format could originate less errors.

The API could also accept:

moduleFor(fullName, callback, delegate)

moduleFor(fullName, delegate)

[dgeb]

With the refactor to use ember-test-helpers, description can now be omitted - see https://github.com/switchfly/ember-test-helpers/blob/master/lib/ember-test-helpers/test-module.js#L7-12