Add a path that may contain available services.
    Return ``True`` if added (or already present), ``False`` on error.

    path
        directory to add to AVAIL_SVR_DIRS

def add_svc_avail_path(path):
    '''
    Add a path that may contain available services.
    Return ``True`` if added (or already present), ``False`` on error.

    path
        directory to add to AVAIL_SVR_DIRS
    '''
    if os.path.exists(path):
        if path not in AVAIL_SVR_DIRS:
            AVAIL_SVR_DIRS.append(path)
        return True
    return False