Add option to make exception format errors fatal.

Adds a new fatal_exception_format_errors config option which
defaults to False. This option is use to control how the base
CinderException class handles errors which can occur when it
formats error messages.

The motivation for this change is to be able to enable exception
format checking in our tests by setting fatal_exception_format_errors=True.

Change-Id: I2df952558d3f30a557cbb094f8bddcc37af9b5aa

cinder/exception.py

@@ -26,10 +26,21 @@ SHOULD include dedicated exception logging.
 
 import webob.exc
 
+from cinder import flags
+from cinder.openstack.common import cfg
 from cinder.openstack.common import log as logging
 
 LOG = logging.getLogger(__name__)
 
+exc_log_opts = [
+    cfg.BoolOpt('fatal_exception_format_errors',
+                default=False,
+                help='make exception message format errors fatal'),
+]
+
+FLAGS = flags.FLAGS
+FLAGS.register_opts(exc_log_opts)
+
 
 class ConvertedException(webob.exc.WSGIHTTPException):
     def __init__(self, code=0, title="", explanation=""):
@@ -114,8 +125,11 @@ class CinderException(Exception):
                 LOG.exception(_('Exception in string format operation'))
                 for name, value in kwargs.iteritems():
                     LOG.error("%s: %s" % (name, value))
-                # at least get the core message out if something happened
-                message = self.message
+                if FLAGS.fatal_exception_format_errors:
+                    raise e
+                else:
+                    # at least get the core message out if something happened
+                    message = self.message
 
         super(CinderException, self).__init__(message)