Permissions improoved. Logging improoved.

1. Renamed utils/errors.py to utils/mfs_exceptions.py.
2. New exceptions added: for metafiles, configs, remote files.
3. Fixed logging in backup_helper and master.
4. Changed option's names in etc/moosefs_tool.ini for config_path and meta_path.
5. Data_path for mounted files in etc/moosefs_tool.ini added.
6. Added field for root password when changing configs.