avocado/core/dispatcher.py: propagate exceptions when running map_method

The dispatcher classes weren't propagating exceptions when running
`map_method`, which is basically how the command line plugins methods
`configure` and `run` are called.

The dispatcher should not be silent about possible exceptions thrown
by plugin's `configure` and `run` methods, so let's fix that.
Signed-off-by: NCleber Rosa <crosa@redhat.com>

avocado/core/dispatcher.py

@@ -27,7 +27,8 @@ class Dispatcher(ExtensionManager):
         self.load_failures = []
         super(Dispatcher, self).__init__(namespace=namespace,
                                          invoke_on_load=True,
-                                         on_load_failure_callback=self.store_load_failure)
+                                         on_load_failure_callback=self.store_load_failure,
+                                         propagate_map_exceptions=True)
 
     @staticmethod
     def store_load_failure(manager, entrypoint, exception):