Add missing test for ErrorHandlingURLopener

I forgot to add this with commit
df9cfda52e952bb4d69cc0ee724e713cd6f468d5
Fix baker to address failing tests

Some tests were failing so I fixed bugs in the code that
were causing the failures.

In Roller.build_filters, reporting_level should not be a
field in the common filters.

The tests for the filename() and manifest_filename() methods
needed to be updated to reflect the updated signatures for those
methods since it was changed to a class method.
Fix elections API mocking in MD datasource tests

In a477b3fcfd47d8481c7fad82ca41c19f9eee10b2, openelex.api.elections
is no longer imported as elec_api into openelex.us.md.datasource.
Update the tests to patch openelex.base.datasource.elec_api
instead.
Fix test for transform registry.

In 24016ce74afc83b18197c89f95d260b388e6e309, the value of
transform.validators was changed from a list to an OrderedDict.

Update the tests to reflect this change.