Removed usage of the py3kcompat module

Like mentioned in I8e0b49cdfbddcf2d44a601ad06be2e75897905fc the
py3kcompat module is deprecated and should not be used.

Updated module apiclient from oslo-incubator to use six instead of
py3kcompat.

Change-Id: I22fa2720fee35f70a8683eb0f099573a43347335