workaround to _strptime import issue on py2
workaround to _strptime import issue on py2

This is a workaround to avoid to trigger:
http://bugs.python.org/issue7980

Change-Id: I154d4eca3f5c9350df169b931df3bd5154a487b7
Closes-bug: #1557021

sileht/gnocchi,gnocchixyz/gnocchi,gnocchixyz/gnocchi,leandroreox/gnocchi,sileht/gnocchi,leandroreox/gnocchi