Continue sending docs even with errors when continue_on_error is true
Use scram as default on wire version 3 or higher
Fix tests for default auth mechanism
Merge pull request #535 from mongodb/SCRAM-as-default-2

RUBY-791 Use SCRAM-SHA-1 as default auth mechanism for wire version >= 3
RUBY-835 Make copy_database work with SCRAM-SHA-1 auth mechanism