Show readable messages on apps login error

[gbasolu]

Problem

When an app do a login, if there is an error (username/password missing or incorrect) the login method raise an exception.
This is correct when there is the need to manage it at an higher level, but it is bad when the app is executed from the command line, because it is hard to understand that the problem was just a wrong login instead of something worse.

Solution

every app will have an additional switch "suppress_exception" so that in case of errors they will be showed with a friendly message (eg. "The username is mandatory" or "login info wrong") and the exception will not be shown.

Code suggestion to add in the app:

if self.suppress_exception:
    log.error("Unable to log in")
else:
    Raise("Unable to log in")