Parses the currently mounted devices.

def CheckMounts(filename):
  """Parses the currently mounted devices."""
  with io.open(filename, "r") as fd:
    for line in fd:
      try:
        device, mnt_point, fs_type, _ = line.split(" ", 3)
      except ValueError:
        continue
      if fs_type in ACCEPTABLE_FILESYSTEMS:
        if os.path.exists(device):
          yield device, fs_type, mnt_point