Make the mapped architecture available in pongo2

[stgraber]

For the Ubuntu images at least, the expectation is that the "description" and "architecture" properties in the LXD image include the architecture name as called by the distribution (so amd64 instead of x86_64), but right now I see now way to access this from pongo2.

[stgraber]

To be clear, I actually need both. We could either export the translated architecture directly or export the function we use to translate them, either way works for me.