Autopilot Eventually matcher gives an obscure message inside the Eventually matcher

[Thomi Richards]

The Eventually matcher calls into the DBus interface. If the DBus backend died, we print a stack trace, instead of raising a custom exception. The stack trace is:

Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/unity8/indicators_client/tests/test_battery.py", line 85, in test_auto_bright_switch
    self.assertThat(auto_brightness.checked, Eventually(NotEquals(old_ab_value)))
  File "/usr/lib/python2.7/dist-packages/testtools/testcase.py", line 406, in assertThat
    mismatch = matcher.match(matchee)
  File "/usr/lib/python2.7/dist-packages/autopilot/matchers/__init__.py", line 109, in match
    wait_fun(self.matcher, self.timeout)
  File "/usr/lib/python2.7/dist-packages/autopilot/introspection/dbus.py", line 180, in wait_for
    _, new_state = self.parent.get_new_state()
  File "/usr/lib/python2.7/dist-packages/autopilot/introspection/dbus.py", line 490, in get_new_state
    return self.get_state_by_path(self.get_class_query_string())[0]
  File "/usr/lib/python2.7/dist-packages/autopilot/introspection/dbus.py", line 479, in get_state_by_path
    return cls._Backend.introspection_iface.GetState(piece)
  File "/usr/lib/python2.7/dist-packages/dbus/proxies.py", line 70, in __call__
    return self._proxy_method(*args, **keywords)
  File "/usr/lib/python2.7/dist-packages/dbus/proxies.py", line 145, in __call__
    **keywords)
  File "/usr/lib/python2.7/dist-packages/dbus/connection.py", line 651, in call_blocking
    message, timeout)

We should catch this and raise a better exception instead.

[PS Jenkins bot (ps-jenkins)]

Fix committed into lp:autopilot at revision 558, scheduled for release in autopilot, milestone 1.4