Fix images/scripts/filter-output encoding

Iñaki Malerbarequested to merge
ina/pipeline:filteroutput into master

With old python versions, filter-output was having problems encoding the logs with some non-standard chars.

Setting PYTHONIOENCODING fixes this problem for sys.stdout.write and calling open() with encoding='utf-8' fixes the output.log file writing.

Fixes: #175 (closed)

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