A new way to decide if the type is string instead of by isinstance

py3 doesn't support basestring, so we need a new way to decide if
the type of an object is string. The module 'six' could
help us: isinstance(var, six.string_types).
Reference: amnong/easywebdav#26

Change-Id: I79266a3c5612d3b7cbe7c94d71d8f5a6aa7c03ab

nova/virt/zvm/volumeop.py

@@ -14,6 +14,7 @@
 
 import contextlib
 import re
+import six
 import time
 
 from oslo_config import cfg
@@ -713,7 +714,7 @@ def _extract_connection_info(self, context, connection_info):
                     self._format_fcp_list(fcp_list))
 
     def _format_wwpn(self, wwpn):
-        if isinstance(wwpn, basestring):
+        if isinstance(wwpn, six.string_types):
             return wwpn.lower()
         else:
             new_wwpn = ';'.join(wwpn)