Do not raise NEW exceptions

Raising NEW exception is bad practice, because we lose TraceBack.
So all places like:

except SomeException as e:
    raise e

should be replaced by

except SomeException:
    raise

If we are doing some other actions before reraising we should
store information about exception then do all actions and then
reraise it. This is caused by eventlet bug. It lost information
about exception if it switch threads.

fixes bug 1191730
Change-Id: Ic2be96e9f03d2ca46d060caf6f6f7f713a1d6b82

cinder/tests/test_scality.py

@@ -61,7 +61,7 @@ class ScalityDriverTestCase(test.TestCase):
             os.makedirs(path)
         except OSError as e:
             if e.errno != errno.EEXIST:
-                raise e
+                raise
 
     def _create_fake_config(self):
         open(self.TEST_CONFIG, "w+").close()
@@ -75,7 +75,7 @@ class ScalityDriverTestCase(test.TestCase):
             os.unlink(self.TEST_CONFIG)
         except OSError as e:
             if e.errno != errno.ENOENT:
-                raise e
+                raise
 
     def _configure_driver(self):
         scality.CONF.scality_sofs_config = self.TEST_CONFIG