Test reorg

1. Convention for names and labels on tests.
2. Reorganized python code to avoid use of LD_LIBRARY_PATH. Achieved by:
    * Convention - directory layout should be:
            xxx/python/ert
            xxx/lib
        Where xxx/python must be in PYTHONPATH
    * Some code in ert/__init__.py sets a static path to the lib directory, and the ert libraries are loaded with full path.