RelStorage and PostgreSQL without 'dsn' parameter remove all other keys

[Rudá Porto Filgueiras]

RelStorage support when used with postgresql driver type can be specified in two ways (with and without dsn key).

Ex, with dsn key:

rel-storage =
   type postgresql
   dsn dbname='zodb' user='ruda' host='localhost' password='12345'
   cache-module-name cmemcache
   cache-servers 127.0.0.1:11211

or without dns key:

rel-storage =
   type postgresql
   dbname zodb
   user ruda
   host localhost
   password 12345
   cache-module-name cmemcache
   cache-servers 127.0.0.1:11211

When this last format is used, plone.recipe.zope2instance try to transform all db connection keys to dsn format, but it's also "eating" all other rel-storage keys.
Follow attached a patch to solve this issue, inserting the new 'dsn' key and removing all other db connection keys.