Replaced python execfile with python 3 compatible code

Change-Id: Iffa32b25a6bf541881756cfef0be0978008643f3
Merge branch 'SIMPLEITK-540_DontAlwaysUseEZSetup' into release

* SIMPLEITK-540_DontAlwaysUseEZSetup:
  Replaced python execfile with python 3 compatible code

Change-Id: Ib2c7f6ee8734b73025dd39daa2c4f864b600a68c