VMware: Handle concurrent registrations of the VC extension

During initialization, the Nova compute driver checks whether a
vCenter extension with key 'org.openstack.compute' exists and if
not, it registers one. This is a race condition. If multiple
services try to register the same extension, only one of them
will succeed. The fix is to catch InvalidArgument fault from
vSphere API and ignore the exception.

Change-Id: I92c24709a2f55b601c31a31b9e748f19e7e31984
Closes-Bug: #1704952

nova/tests/unit/virt/vmwareapi/test_driver_api.py

@@ -2055,6 +2055,18 @@ class VMwareAPIVMTestCase(test.NoDBTestCase,
                                                   'find_extension',
                                                   constants.EXTENSION_KEY)
 
+    def test_register_extension_concurrent(self):
+        def fake_call_method(module, method, *args, **kwargs):
+            if method == "find_extension":
+                return None
+            elif method == "register_extension":
+                raise vexc.VimFaultException(['InvalidArgument'], 'error')
+            else:
+                raise Exception()
+        with (mock.patch.object(
+                self.conn._session, '_call_method', fake_call_method)):
+            self.conn._register_openstack_extension()
+
     def test_list_instances(self):
         instances = self.conn.list_instances()
         self.assertEqual(0, len(instances))