Add tests/ directory shipped by OCCT 6.7.0
Add support for OCCT tests in CMakeLists.txt

In order to run tests before installing, copy
all DLLs into the same directory, and use a
wrapper to set environment variables.
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.
Fix generation of DrawLaunchTests.cmake

PATH variable was not set to its expected value.
Add an OCE_SKIP_TESTS_DATA environment variable when running OCCT tests

This variable let locate_data_file exits quickly, as we know we
do not have data files.  This speeds up processing SKIPPED tests.
Do not set CSF_TestScriptsPath environment variable

Tests are already searched in the $CASROOT/tests directory; by setting
CSF_TestScriptsPath, tests are run twice.
Set CSF_XCAFDefaults in DrawLaunchTests.cmake

This fixes several test failures about xcaf.
Rename OCE_TCL_TEST_LIST option into OCE_TCL_TEST_GROUP

Running several testgrid commands in the same draw script does
not work, results are not concatenated.  So let user choose only
one single group.