- Fix the snapshot name, it is not "portage-${VERSION}", but rather
"gentoo-${VERSION}".
- After building the snapshot, remove all the similar files from the
snapshots directory - Catalyst gets easily confused by them and
bails out.
- Extend the `build_snapshot` function to optionally accept the config
path and the snapshot name, so SDK's stage1 code can use this
function instead of duplicating parts of it.