Virt dirsearch

These changes allow for arbitrary organization of both config. and test module files.  All glob matching files in all subdirectories beneath a particular root are returned and processed as a flat list.  There is also some result filtering to ensure the config. dirs can't contain test modules, and test module dirs can't contain config. files. 

I'm not certain the data_dir module is the best place for the new classes, but the location isn't terribly important.

Tested with latest Next on RHEL 5 from autotest client, test runner, and get_started.py (after moving some cfg and test modules around).