oci_tarball: set time, user and group to reproducible values for Linux

[gergelyfabian]

Applied suggestion for Linux from:

http://h2.jaguarpaw.co.uk/posts/reproducible-tar/

Left out MacOS and other systems for now (waiting for tar toolchain).
MacOS does not have the same options for tar, for now fixing this only
for Linux.

[gergelyfabian]

Follow up for #380.

[chancila]

this is a gnu tar flag, this won't work on other tars...for reference bsd/mac tar uses --uname and --gname

[alexeagle]

We'll fix this after we have bazel-contrib/bazel-lib#468 so the same hermetic tar is used everywhere.

[gergelyfabian]

Rebased PR with the revert for #380.
Updated to set parameters only for Linux (I could also set parameters for Mac, but I don't have a way to test it, so preferred to leave the functionality unchanged for Mac). Optimally it would be better to use the tar toolchain (bazel-contrib/bazel-lib#468), but not having reproducible tars is a regression when migrating from rules_docker to rules_oci, so I'd personally prefer to have it fixed in the meantime.

[alexeagle]

Sorry, I'd rather not merge a fix that's only for one platform, that just leaves both the original bug and also some tech debt for us to remove. #385 is probably the better change, though it may take a couple weeks to land. I suggest you apply this patch in your own repo for now.

[gergelyfabian]

Sure. Is #385 already dealing with reproducible tars or it's just starting to use the tar toolchain?

[alexeagle]

The tar rule in bazel-lib should already be reproducible, that's part of its API contract.

However in that PR I'm just using the toolchain directly, so it will need some flags set, you're right.

[alexeagle]

okay I updated that PR with halfway working implementation that uses an mtree file to exactly specify deterministic content of the tar file.

Not sure when @thesayyn or I will get time to finish it...

[gergelyfabian]

Thank you! Let me know if I can help in any way (I could contribute something if necessary). Surely I will test this implementation.

[gergelyfabian]

Can confirm that #385 already implements reproducible tars.