Correct ceilometer reraising of exception

When an exception was caught and rethrown, it should call 'raise'
without any arguments because it shows the place where an exception
occured initially instead of place where the exception re-raised.

Change-Id: Ie975b938dbc5d6886ccc83f6897aa4c8dea1cdee

ceilometer/hardware/pollsters/generic.py

@@ -113,7 +113,7 @@ class GenericHardwareDeclarativePollster(plugin_base.PollsterBase):
                 LOG.exception(_LE("Cannot load inspector %(name)s: %(err)s"),
                               dict(name=parsed_url.scheme,
                                    err=err))
-                raise err
+                raise
         return self.inspectors[parsed_url.scheme]
 
     def get_samples(self, manager, cache, resources=None):