[#56813978] Chorus can connect to SSL-enabled Greenplum databases.

 The data source new/edit form has a 'Use SSL' checkbox that will set the appropriate options.

 Fixed up GreenplumIntegration tests to always go through Sequel (which respects
 the SSL flag) rather than ActiveRecord::Base.connection.
 Set ssl flag in test data source yml file to run integration tests vs an SSL instance.