Refactor the lookup tables to be more flexible and DRY

This takes the templates for the transport map table and sasl_passwd lookup
table and replaces them with a single template. The templates were already
nearly identical and we would have needed to create more duplicates for every
new lookup table we implemented.

Also, the 'postfix__transport_map' and 'postfix__smtp_sasl_password_map'
variables have been replaced with a single dictionary 'postfix__tables' where
each key in the dictionary is the name of the lookup table, and the value is a
dictionary of entries for that lookup table. By using a dictionary we can
implement default lookup tables per operationg system and then allow downstream
additions or overrides via combining the dictionary with a new dictionary
instead of having to redefine the entire thing to override a single value.