Use [info nameofexecutable] to retrieve DRAWEXE path

This is to ensure that tests are run with the right DRAWEXE
executable, and not the first one found in PATH.
Also look for textures in installation path

Handling of texture directory had been reworked in OCCT 6.6.0,
and as a consequence our changes in order to get rid of CASROOT
were now incomplete.
Bugfix: dumped PPM images were wrong if width != height
In savePPM, write row by row, it should be faster than byte by byte
Add support for OCCT tests in CMakeLists.txt

Copy all DLLs into adm/cmake/DRAWEXE/ directory and
set environment variable.
Add more variables into DrawLaunchTests

Remove OCE_INSTALL_DATADIR, it is not needed after all, CASROOT
can be used instead.

To be safe, run tests in sequential for now.