tar: Make all gzip compression hermetic

[DolceTriade]

We weren't passing the flag to make gzip hermetic. Without the flag to
ignore timestamp, the shasum will differ based on the system time.

Also, DEFAULT_ARGS contained "--options=gzip:...", which is invalid when
using any other compression scheme. Therefore, remove that option from
DEFAULT_ARGS and provide an alternate function called
add_default_compression_args to add per-compression type default
arguments which can do things like make the compression more hermetic.

Repro instructions:

bazel test //...
find -L bazel-bin -name "*.gz" -exec sha256sum {} \; > sha
bazel clean --expunge
bazel test //...
sha256sum -c sha

Before, the above test would fail with sha256sum mismatches. With this patch, all shasums match.

[thesayyn]

Thanks!

[DolceTriade]

tar: Unknown module name: `gzip'

Hm, I thought that the aspect build tar would support this universally?

[DolceTriade]

Ok, tests pass now. While running I realized a lot more than flatten was not hermetic, so I fixed those as well. Please let me know if you'd like a different approach. I also updated the commit message with the motivations.

[jjmaestro]

I'd love to get this merged, I'm also using flatten and will need the hermeticity! :)

[thesayyn]

@DolceTriade could you rebase and solve the merge conflicts? there are also some buildifier issues it seems

[DolceTriade]

Done. @thesayyn PTAL, thanks!

[DolceTriade]

I'm guessing the buildifier failures are due to differing versions of buildifier...

[DolceTriade]

Hm, nvm, I didn't even modify the file in question?

[jjmaestro]

Yeah, the buildifier errors are due to other PRs, I've fixed it in #108