Support new env variable for tests : SALOME_TESTS_PATH and SALOME_TESTS_DIRECTORY
SALOME_TESTS_PATH is a list of path separated with a ";" or ":"
If given, a new CtestTestfile.cmake file is created in SALOME_TESTS_DIRECTORY.
If SALOME_TESTS_DIRECTORY is not provided, a temporary directory is created instead.
The temporary directory is deleted after the tests execution.
If SALOME_TESTS_PATH is not provided, the previous behaviour is kept (run tests in ABSOLUTE_APPLI_PATH/bin/salome/test).
