Update test exercising broken proxy behaviour.

The test must account for the fact that the connection
will be retried with TLS_MODE_COMPATIBLE if the first
attempt throws an exception.

It's also worth noting that MockWebServer does not
deal with abrupt client disconnections in a particularly
graceful manner (but that does not affect the test,
and I'll address it in a follow up).

(cherry picked from bfdb88fab84756703e01e9b43808a406bdd)

bug: 10211309

Change-Id: I5bf8a8e890df4146ecd0606e50c5a616434fd883
1 file changed