mas mirror-images should allow you to choose your architecture

[BrendanFishback]

Feature and motivation

Currently, when running mas mirror-images it will download images for all three architectures which uses up a lot of space and download time for clients. There should be a variable which would allow you to choose which architecture you are using and limit the downloads to that specific architecture.

Usage example

The variable could be something simple like '--arch' that is passed during execution to limit which architecture is used for downloading the images. It could also be offered as an option during the interactive version as well.