Add facility to borg-backup role to run a command and save the output
of it to a separate archive file during the backup process.
This is mostly useful for database backups. Compressed on-disk logs
are terrible for differential backups because revisions have
essentially no common data. By saving the uncompressed stream
directly from mysqldump, we allow borg the chance to de-duplicate,
saving considerable space on the backup servers.
This is implemented for our ansible-managed servers currently doing
dumps. We also add it to the testinfra.
This also separates the archive names for the filesystem and stream
backup with unique prefixes so they can be pruned separately.
Otherwise we end up keeping only one of the stream or filesystem
backups which isn't the intention. However, due to issues with
--append-only mode we are not issuing prune commands at this time.
Note the updated dump commands are updated slightly, particularly with
"--skip-extended-insert" which was suggested by mordred and
significantly improves incremental diff-ability by being slightly more
verbose but keeping much more of the output stable across dumps.
Change-Id: I500062c1c52c74a567621df9aaa716de804ffae7
51733e5623