[toolsutils] Small fixes to fill_templated_file() * Use context managers to close _both_ files * Use io.open to enforce text mode on both python 2 and 3

usr/bin/cubicweb-ctl usr/bin/
usr/lib/python2*/*-packages/cubicweb/cwctl.py
../cubicweb-ctl.bash_completion etc/bash_completion.d/cubicweb-ctl