* HTTP error 500 occurs with Exchange 2003 when the user tries to
authenticate with wrong credentials; we report this as "Cannot
connect to server", which is wrong
* Error 500 is supposed to mean "internal server error", but since
we know that an authentication error can cause this, we now put
up a better error message
Bug: 2933381
Change-Id: I9319a5ed6fbf4c92739f305b42b6b1cad7036a4b