Improve get_process_golang_version()

[Jongy]

The function accepts a psutil.Process and reads its /proc/pid/exe. It is cached on a per-Process basis, but Processes replace often and we can do smarter caching based on modification time of the absolute path of /proc/pid/exe based on the mnt ancestor, so /proc/{get_mnt_ns_ancestor(process)}/root/path/to/exe.

[marcin-ol]

I think it would be an improvement, but how do we know if we're referring to the right version of the exe file?

Let's assume I start ./helloworld as pid1, and N minutes later ./helloworld as pid2.

• what if I upgrade the original ./helloworld on disk, between starting pid1 and pid?
  • Process(pid1).exe() will report the original exe path for pid1 and pid2; in procfs, /proc/pid1/exe will read ./helloworld (deleted) for pid1.
• what if I upgrade the original ./hellworld on disk, but pid2 is a fork of pid1?
  • Process(...).exe() will report original path for pid1 and pid2, but in procfs we will see ./helloworld (deleted) for both pids; our caching won't be able to tell they both refer to the same exe, and will report incorrect version for pid2, right?

I think we need to look up modification time for exe file matching (not younger than) the create_time of the process. This should help with first bullet above, but not with forked processes.