clean up

[joachimmetz]

• remove "The default is" in docstrings where not needed
• Changes to docstrings and source to match style guide
• use path spec factory in tests instead of individual path spec classes - moved to use path spec factory in tests instead of individual path spec classes #535
• check if _file_object_set_in_init is used, otherwise remove
• move LOCATION_ROOT to file system base class
• check and implement GetParentFileEntry
  • implement for tsk_partition_file_entry.py
• add tests for analyzers
• change def _Open(self, path_spec=None, mode='rb'): to def _Open(self, path_spec, mode='rb'):