fix ConsentTest

Includes the following changes:

* Fix TestUserHelper to create accounts with bridge-testing+[semi-unique token]@sagebase.org. This is so test emails don't impact our SES bounce rate.

* Make BaseApiCaller.toQueryString() URL encode query param values. Otherwise, they get garbled by the server. (Specifically, the +'s in test email addresses.)

* Re-enable ConsentTest.