auth: don't use an Unicode literal, they're not supported in Py 3.2

Use port.to_u instead.
mixpanel/tests: make sure to pass unicode to json.loads

In Python 3.x json.loads only accepts unicode objects.
ducksboard: don't use None for the password in Basic Auth

The filter expects a string, so make up one instead of using None.
tests: add some tests for the Basic Auth filter