Parse the passwd file.

def Parse(self, stat, file_object, knowledge_base):
    """Parse the passwd file."""
    _, _ = stat, knowledge_base
    lines = [
        l.strip()
        for l in utils.ReadFileBytesAsUnicode(file_object).splitlines()
    ]
    for index, line in enumerate(lines):
      user = self.ParseLine(index, line)
      if user is not None:
        yield user