According to pep-0263, python scripts can define encoding magic on
first or second line.
If we use for example such a script:

```python
  # coding: utf-8
  return "héhé"
```

then using .read() was wrong, because it return the script with headers,
ie:

```python
  ## Script (Python) "test_coding"
  ##bind container=container
  ##bind context=context
  ##bind namespace=
  ##bind script=script
  ##bind subpath=traverse_subpath
  ##parameters=
  ##title=
  ##
  # coding: utf-8
  return "héhé"
```

so the coding magic is no longer in first line and pylint complains
with error like:

Cannot decode using encoding "ascii", unexpected byte at position 11 (invalid-encoded-data)]

/reviewed-on !825