Ensure that the job.out and job.err files are listed for jobs running on platforms with a configured tailer command even if the file is not yet present in the job log directory.

Explanation:

• The cylc cat-log command can be used to retrieve job logs.
• The -m l option tells cat-log to list the available job log files.
• The Cylc UI Server uses the -m l option to populate the dropdown of available log files.
• Some platforms have a funny setup where the job.out and job.err files are moved into the job log directory after the job has completed. Until this point they live on a compute node somewhere so do not appear in the -m l listing.
• To allow users to access these files whilst the job is still running the batch system provides a command.
• Cylc provides support for these setups using the "tailer" options, these allow system administrators to configure the batch system command to view the files.
• So in these situations, the job.out and job.err files are viewable via the configured "tailer", however, they don't appear in the file system listings (because they haven't been moved into the job log directory yet).
• To get around this we should add some logic to cylc cat-log which:
  • Adds job.out and job.err to the list of files returned by cylc cat-log -m l,
  • if the job is running (as determined from the database),
  • and there is a "tailer" configured for the platform (as determined from the platform configuration).
• We are (apparently) already performing database access somewhere in cylc cat-log so this should be a matter of hooking this extra logic into that check.