test(NFS): run either nfsv4 or nfsv3 tests

[Henrik66]

Run only nfsv4 tests unless nfs4 is not available

Checklist

• [X] I have tested it locally
• [ ] I have reviewed and updated any documentation if relevant
• [X] I am providing new code and test(s) for it

Fixes #2455

[LaszloGombos]

This is a discussion meant to focus on what is running on CI (and not what can or should be tested outside of CI). Currently Test 20 is longest running and most likely to timeout test on our CI (with 45 min timeout). Only enabled on Fedora.

To get to a state where CI is green and/or we enable this test for other distributions also, we need to either:

• make the test do less things and finish earlier (this is what this current PR proposes)
• increase timeout for the test (not a good option)
• parallelize subtests instead of running them sequentially (will take a while to come up with a way to do so)

CC @bdrung for visibility and feedback.

@bdrung what do you think of the goal of this PR and/or the way it is trying to do it ? Is there a better way to detect installed NFS versions in a distribution agonistic way ?

[bdrung]

The first question to answer is: Do we want to run only NFS v3 or v4 tests? How widely used is NFS v3 vs v4? If v3 is legacy and most of all systems use v4, I am fine with only running v4 tests (if v4 support is available). Other having tested both would be preferred.

[LaszloGombos]

The first question to answer is: Do we want to run only NFS v3 or v4 tests? The current Gentoo test container only supports NFS v3. All other test containers support NFS v4.

I am fine with only running v4 tests (if v4 support is available). Other having tested both would be preferred. Me too - this is what this PR is proposing already.