GlideinWMS

Glideins allow implicit and explicit <files> files to be downloaded and executed if desired.
All these scripts are

• before the condor invocation
• periodic script run also periodically while condor is running

There is a need to have some scripts (at least one) run also after condor completes to perform cleanup operations
This could use a mechanism similar to GLIDEIN_LAST_SCRIPT, e.g. adding the attribute GLIDEIN_CLEANUP_SCRIPT, and have a variable point to a script that is singled out to run after the condor invocation instead of before it like all other setup scripts.

This would allow a cleaner implementation of mechanisms like cvmfsexec using mountrepo/umountrepo.

NOTES:

• the script should still be downloaded at the beginning (same checksum and download mechanisms)
• the script could invoke other scripts. This could be a standard mechanism advertised in the instructions and used also by operators or something internal available only for GWMS developers. E.g. another attribute w/ an ordered list of scripts to run? Or GLIDEIN_LAST_SCRIPT being a list instead of one name?
• state clear error conditins: if the script is missing (or the download fails) will the glidein fail? or run w/o executing it? It there is an error what should be the glidein execution status? How can problems be reported? Standard error_gen mechanism?