Raise specific exception for an invalid protocol connector

Nova's libvirt driver attempts to load up a set of volume
drivers which use os-brick connectors on start of the
nova-compute service. If there is a missing or invalid
mapping, like ISER + s390x, it results in a ValueError and
nova-compute fails to start.

This change raises a specific exception, which is still a
ValueError for backward compatibility, so that Nova can
handle this situation gracefully and not crash.

Change-Id: I1d016c226416cf2b77d6e0393498905f56fd8cde
Partial-Bug: #1639239
(cherry picked from commit f7b8d242f7)

os_brick/exception.py

@@ -154,3 +154,8 @@ class InvalidIOHandleObject(BrickException):
 class VolumeEncryptionNotSupported(Invalid):
     message = _("Volume encryption is not supported for %(volume_type)s "
                 "volume %(volume_id)s.")
+
+
+# NOTE(mriedem): This extends ValueError to maintain backward compatibility.
+class InvalidConnectorProtocol(ValueError):
+    pass

os_brick/initiator/connector.py

@@ -29,6 +29,7 @@ from oslo_concurrency import lockutils
 from oslo_log import log as logging
 from oslo_utils import importutils
 
+from os_brick import exception
 from os_brick.i18n import _
 from os_brick import initiator
 from os_brick import utils
@@ -270,7 +271,7 @@ class InitiatorConnector(object):
             msg = (_("Invalid InitiatorConnector protocol "
                      "specified %(protocol)s") %
                    dict(protocol=protocol))
-            raise ValueError(msg)
+            raise exception.InvalidConnectorProtocol(msg)
 
         conn_cls = importutils.import_class(connector)
         return conn_cls(*args, **kwargs)

os_brick/tests/initiator/test_connector.py

@@ -19,6 +19,7 @@ import mock
 from oslo_concurrency import processutils as putils
 from oslo_log import log as logging
 
+from os_brick import exception
 from os_brick.initiator import connector
 from os_brick.initiator.connectors import base
 from os_brick.initiator.connectors import fake
@@ -225,7 +226,7 @@ class ConnectorTestCase(test_base.TestCase):
         obj = connector.InitiatorConnector.factory("disco", None)
         self.assertEqual("DISCOConnector", obj.__class__.__name__)
 
-        self.assertRaises(ValueError,
+        self.assertRaises(exception.InvalidConnectorProtocol,
                           connector.InitiatorConnector.factory,
                           "bogus", None)