Use flake8-import-order

Use the flake8 plugin flake8-import-order to check import ordering. It
can do it automatically and don't need reviewers to check it.

Change-Id: Ia3d81bbbb44b40804b3268c0e648276a36cb4805

nova/api/metadata/vendordata_dynamic.py

@@ -15,13 +15,13 @@
 
 """Render vendordata as stored fetched from REST microservices."""
 
-import six
 import sys
 
 from keystoneauth1 import exceptions as ks_exceptions
 from keystoneauth1 import loading as ks_loading
 from oslo_log import log as logging
 from oslo_serialization import jsonutils
+import six
 
 from nova.api.metadata import vendordata
 import nova.conf