improve pg_hba.conf template flexibility and consistency

We need the ability to set UNIX domain socket (local) acls in the pg_hba.conf.
The usage of two string variables (ip_mask_deny_postgres_user &
ip_mask_allow_all_users) to set special acl rules along with with lists
(ipv4acls, ipv6avls) was highly non-orthogonal.

This patch removes from postgresql::{params, config, config::beforeservice}

$ip_mask_deny_postgres_user
$ip_mask_allow_all_users

And moves the ACLs created by those two vars into
$postgresql::params::ipv4acls.  It adds a new variable
$postgresql::params::unixacls which replaces one of the hard coded unix domain
socket rules in pg_hba.conf.erb.  In addition, it removes the usage of
tabstops in pg_hba.conf.erb and makes the indentation more consistent.  One of
the major motivations of this patch is to get the use the ability to remove
almost all of the ACLs.