Ticket #48252 - (lib389) adding get_bin_dir and dbscan
    
    Description: Adding APIs:
    - get_bin_dir(sroot=None, prefix=None)
      returns <prefix>/usr/bin
    - dbscan(self, bename=None, index=None, key=None)
      runs dbscan -f /path/to/db/bename/index{.db} [-k key | -K key]
      If index does not contain ".db", ".db" is added.
      If index is id2entry and key is digit, key is translated to "-K key".
      If index is not id2entry, key is translated to "-k key".
    
    https://fedorahosted.org/389/ticket/48252
    
    Reviewed by mreynolds@redhat.com (Thank you, Mark!!)