Handle role::labs::instance properly in pmtpa.

role::labs::instance is included in eqiad labs instances
instead of ldap::role::client::labs.

So, in tampa, explicitly include role::labs::instance in base,
and exclude ldap::role::client::labs from role::labs::instance so
it isn't included twice.

Change-Id: Id74fbda21fb894dda11d7c590701c087ca745fc7