Don't raise unnecessary stack traces in EC2 API

exception.EC2APIError exceptions are always expected, so no reason to have a
LOG.exception when one is raised.  Furthermore nova.api.ec2.ec2_error already
logs the exception so the duplicate log statement is just removed

Fix Bug 1180973

Change-Id: I4b42a9a764f6e15bb94a383e8a725d52d7436bd7

nova/api/ec2/__init__.py

@@ -501,8 +501,6 @@ def __call__(self, req):
             LOG.info(_('NotFound raised: %s'), unicode(ex), context=context)
             return ec2_error(req, request_id, type(ex).__name__, unicode(ex))
         except exception.EC2APIError as ex:
-            LOG.exception(_('EC2APIError raised: %s'), unicode(ex),
-                          context=context)
             if ex.code:
                 return ec2_error(req, request_id, ex.code, unicode(ex))
             else: