feat(build_packages): Add --upload option to build_packages

Defaults to upload for official builds and not otherwise.
fix(bootstrap_sdk): Remove seedcache and snapcache features.

We aren't taking full advantage of seedcache and untarring things isn't
a big burden on us anyway so don't bother and hopefully avoid leaving
oodles of files behind.
Merge pull request #20 from marineam/target

Add ability to upload amd64-generic packages