Temp. fixes wsme problem with six v1.4.0

Fixes wsme problem with six version 1.4.0.
Limits six version to <1.4.0 in requirements.txt

This can be lifted after https://review.openstack.org/#/c/44659/
is merged and new wsme is released.

Change-Id: Iad888ea9a18eb10eacefed0419787153ee35126e
Merge "Temp. fixes wsme problem with six v1.4.0"