lib/param: Create a seperate server role for "active directory domain controller"

lib/param: Create a seperate server role for "active directory domain controller"

This will allow us to detect from the smb.conf if this is a Samba4 AD
DC which will allow smarter handling of (for example) accidentially
starting smbd rather than samba.

To cope with upgrades from existing Samba4 installs, 'domain
controller' is a synonym of 'active directory domain controller' and
new parameters 'classic primary domain controller' and 'classic backup
domain controller' are added.

Andrew Bartlett