In progress: snapcraft 2.30

[elopio]

While reviewing and polishing PRs, we worked on a few utf-8 issues.

We have this bug:
snapcraft fails if desktop file included “ascii” cannot decode byte

It highlights a few issues:

• We are not setting utf-8 as the locale in our cleanbuild containers: PR #1304
• We are not reading and writing the desktop files as utf-8: PR #1309
• We don’t need our docker container to have en_US locale: PR #1310