Fix "defaultContainer is no longer supported" deprecation warning

Fixes `Using the defaultContainer is no longer supported. [defaultContainer#lookup]` deprecation warning

The fix is based on https://gist.github.com/stefanpenner/5627411 and modelled after similar fix to ember-table: https://github.com/addepar/ember-table/commit/1fd29fdb2ae5283a7664f83789cc6b3550a5eb3c