Remove usage of module py3kcompat

Module py3kcompat was removed from oslo-incubator. We need remove its
usage in client side firstly. This make us move smoothly when sync
oslo-incubator code.

Change-Id: I8b07c32c9852e747579a23685f3c8a07ac13ec01
Partial-Bug: #1280033
Merge "Remove usage of module py3kcompat"