Make clone cleanups more robust

[2opremio]

• Fixes a systematic clone leak (introduced in Read-only mode #1807 , released in 1.14 ) in every bump of the sync tag. This probably justifies a new patch release and it probably fixes Flux may be leaking files in /tmp #2713 . I still don't understand how this has escaped our radar until Flux may be leaking files in /tmp #2713
• Removes the temporary cloning directory if git clone fails for whatever reason
• It stops hiding underlying errors inExport.Clean() and prints them wherever a logger is available (not perfect, but better).

[2opremio]

As a future optimization, we don't really need a working directory for bumping and pushing the tag, which would save quite a bit of space in big repos (e.g. in #2713 ~1GB of data would be saved)

[hiddeco]

Given the fact that the errors were silenced and a repository with just YAMLs shouldn’t be really big in size for most clusters, I can understand why we didn’t notice earlier.

Looks good to me, thanks Fons 🎖

[squaremo]

we don't really need a working directory for bumping and pushing the tag

You do need to have the changed tag visible locally only when it has been pushed to the upstream repo, though.

[squaremo]

Looks reasonable, thanks Fons. I honestly cannot remember why the clone was not cleaned up -- I either persuaded myself that it was not necessary, or I just forgot. Owps!