More retention policies

[CharlesMAtkinson]

Currently most bung scripts have a configuration option retention=days which makes them remove backups older than that number of days

On a computer which is run infrequently, that could result in removing all old backups. If there is plenty of backup file system space there is no benefit in removing more old backups than necessary to ensure space for the next backup

This issue is to add retention=% to make the scripts progressively remove the oldest backups until the backup file system % used is less than the specified percentage

The affected scripts are mysql_bu, openldap_bu, postgres_bu, rsync_bu, sysinfo_bu and templated_bu

[CharlesMAtkinson]

The issue was extended to add retention=<number>percent_usage[,<number>min_old_backups] and retention=<number>old_backups

[CharlesMAtkinson]

Closed by version 3.3.0