The officially supported workflow for the CLI is to use only the default emulator.
As you found out, however, there is code which slipped through and can be changed to support running on a particular emulator image. In its current state, this code is unfinished and that's why it is undocumented.
Your change makes it work, but this is only a temporary measure. You can use it but we cannot guarantee its stability. We plan to implement this feature more thoroughly for our next release. If this happens, the feature will also be tested, fully supported and well documented.
In the meantime, I would like to thank you for bringing it to our attention. As a small token of our gratitude I updated your Telerik points.