Revert "Run unit tests in tripleo-image-elements"

This reverts commit cdd09d30731678c99b5f20196145899af5cc1b35.

The gate for tripleo-image-elements is broken due to this commit. We
need to fix doc building and python26 before this will pass.

Change-Id: Icf02d05ff1e6f455b65c123a1091d4d32e6dbf1f
Merge "Revert "Run unit tests in tripleo-image-elements""