administration: fix BT's "Check Python Code" with coding flag
According to pep-0263, python scripts can define encoding magic on first or second line. If we use for example such a script:
# coding: utf-8
return "héhé"
then using .read() was wrong, because it return the script with headers, ie:
## 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)]