python/samba/gp_parse: PY2/PY3 compat changes for __init__.py

python/samba/gp_parse: PY2/PY3 compat changes for __init__.py

Fixes.

1) sorting of xml.etree.ElementTree.Element, in PY2 sort
   seems to sort lists of these. In PY3 this no longer works.
   Choosing tag as the sort key for py3 so at least in python3
   there is a consistent sort (probably won't match how it is
   sorted in PY2 but nothing seems to depend on that)
2) md5 requires bytes
3) tostring returns bytes in PY3, adjust code for that

Signed-off-by: Noel Power <noel.power@suse.com>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>