Non-account backups should honor pigz compression preference

Pigz compression should be used for all backups, not just account packaging:

Per case 68061, pigz is not used for important configuration files nor any directory backups outside of cPanel account backups.

Example use case, based on a cPanel support request:

A real scenario where pigz should have offered significant improvement is a very sizable MySQL data directory, in this case at 59 GB of disk usage. When gzip was used, the backups ran for 9 hours generating server load before being forcefully killed to return the system back to normal operation.