[Feature] Add 'list' option to `fail2ban.py whitelist`

[JohnMertz]

This issue is being imported from our ticketing system to better centralize all feature requests and bug reports.

There is currently no way to list the existing whitelists using the fail2ban.py executable. This information is available within the jail.d file after dum_firewall.pl is run, or from fail2ban_ips table in mc_config with whitelisted = 1.

After running 'add' it prints the list, including the new entry, so an existing function should already exist (or can be easily separated out), we just need to add a 'list' option the whitelist command.