Tests: fail on every failure.

Travis was reporting a failure where the local run wasn't.  This turns
out to be due to a difference in default `error_reporting`.

We want to find as many bugs as possible, so now anything remotely like
an error is reported as one.
Fix silly tests error.

The from number for Twilio is required, even if we're not actually using
Twilio in the tests, because we pass it along to the (mocked)
sms-sender.