Fix test_dialer

This is a version of test_dialer that should work. It was originally contained in the pull request for call_log, but that one is still outstanding wrt populating the call log, so I figured I should submit this separately. Note that to run this you'll need to provide a ```phone_number``` in the new ```twilio``` section of the testvars file. For now you can use the number associated with the test account I created, which is +12195953076.