CI systems and opam versions

[hannesm]

I'm not sure where this issue or discussion belongs, but from what I see it that "opam-repo-ci" takes an arbitrary opam version (or the master branch, it is very hard to inspect what is used) in the workers.

From my point of view, the CI would be great if it would just use the default opam that someone will install on such a system. So, just the one that is provided by the package system. The idea behind this is that opam-repo-ci should IMHO observe failures before a developer observes them -- and for this it is crucial to have the same environment.

Of course, I'm a big fan to test the latest release of opam (and earlier versions of opam) explicitly, as am I sure that testing the main branch of opam is worth it (for opam developers to quickly observe regressions).

What do you think?

With the same idea, it would still be great to include e.g. in macos and FreeBSD workers the OS version (see ocurrent/opam-repo-ci#277).