testsuite - improve the way we find OIIO
testsuite - improve the way we find OIIO

If OPENIMAGEIOHOME is not found in the environment, assume the binaries
we need are in the execution search path.

yaroslav-tarasov/OpenShadingLanguage,gzorin/OpenShadingLanguage,amartinez-cg/OpenShadingLanguage,svenstaro/OpenShadingLanguage,lgritz/OpenShadingLanguage,amartinez-cg/OpenShadingLanguage,mcanthony/OpenShadingLanguage,johnhaddon/OpenShadingLanguage,aconty/OpenShadingLanguage,imageworks/OpenShadingLanguage,aconty/OpenShadingLanguage,brechtvl/OpenShadingLanguage,brechtvl/OpenShadingLanguage,johnhaddon/OpenShadingLanguage,lgritz/OpenShadingLanguage,svenstaro/OpenShadingLanguage,imageworks/OpenShadingLanguage,gzorin/OpenShadingLanguage,svenstaro/OpenShadingLanguage,imageworks/OpenShadingLanguage,yaroslav-tarasov/OpenShadingLanguage,aconty/OpenShadingLanguage,mcanthony/OpenShadingLanguage,amartinez-cg/OpenShadingLanguage,sjparker/OpenShadingLanguage,juvenal/OpenShadingLanguage,amartinez-cg/OpenShadingLanguage,brechtvl/OpenShadingLanguage,yaroslav-tarasov/OpenShadingLanguage,fpsunflower/OpenShadingLanguage,fpsunflower/OpenShadingLanguage,gzorin/OpenShadingLanguage,fpsunflower/OpenShadingLanguage,rlmh/OpenShadingLanguage,imageworks/OpenShadingLanguage,imageworks/OpenShadingLanguage,lgritz/OpenShadingLanguage,mcanthony/OpenShadingLanguage,amartinez-cg/OpenShadingLanguage,sjparker/OpenShadingLanguage,johnhaddon/OpenShadingLanguage,gzorin/OpenShadingLanguage,rlmh/OpenShadingLanguage,aconty/OpenShadingLanguage,rlmh/OpenShadingLanguage,sjparker/OpenShadingLanguage,aconty/OpenShadingLanguage,brechtvl/OpenShadingLanguage,svenstaro/OpenShadingLanguage,juvenal/OpenShadingLanguage,gzorin/OpenShadingLanguage,yaroslav-tarasov/OpenShadingLanguage,mcanthony/OpenShadingLanguage,juvenal/OpenShadingLanguage,brechtvl/OpenShadingLanguage,fpsunflower/OpenShadingLanguage,lgritz/OpenShadingLanguage,lgritz/OpenShadingLanguage,johnhaddon/OpenShadingLanguage,juvenal/OpenShadingLanguage,rlmh/OpenShadingLanguage,sjparker/OpenShadingLanguage