sgcollect: Re-gzip rotated logfiles post-redaction, clean up intermediate extracted files

When we extract rotated log files, we extract them to perform log redaction on them, and leave them in an extracted state lying around in /tmp for the duration of the sgcollect_info run before putting them into the final zip.

This seems to be counter to what was done in CBG-244, but here's an example with around 6GB of pre-compression logs:

There are a couple of things we can do to optimise the collection of rotated logs:

1. If we're not performing log redaction, skip the extraction step completely. Put the .gzip files straight into the zip file as-is.
2. If we are performing redaction:
   1. extract
   2. redact
   3. re-compress
   4. put the newly redacted/compressed file into the zip file
   5. Make sure the extracted files are cleaned up as we iterate over each log file, to reduce the overall disk requirements.