Clean up unused directories under jobs on the jenkins server

[sxa]

Extracted from #2108 (comment)

We have a lot of jobs not in the UI but are on the file system. This seems to be because the config.xml has gone but the job directory is still present (Maybe due to artefacts being kept after job deletion?). These can be identified with for A in *; do if [ ! -r $A/config.xml ]; then ls -ld $A; fi; done in the jobs directory - at the time of writing there are 1695 without a config.xml (directly under jobs) of which all but 195 are Test_openjdk ones.

897 of these are @script directories as opposed to job directories that mostly contain extracted copies of openjdk-tests (Now an obsolete name). Of the 2736 @script ones, 689 have a corresponding job named the same, so over 200 do not. Only one of those 689 (Grinder_perf) is missing a config.xml.

There are also 15 @tmp suffixed directories and six @libs

None of the analysis above covers anythign that might be in subfolders.

I suspect we should clean up all of the @script directories (The most recently updated one was from 2021) and also have a backup/purge on all other directories without a config.xml