This allows to not hardcode connection strings in testArchive and
testERP5Catalog, which need several databases.

A new environment variable (extra_sql_connection_string_list) is recognized:
it is a colon-separated string of connection strings.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@30863 20353a03-c40f-0410-a6d1-a30d3c3de9de