Don't use parallel jobs for pylint

When pylint runs in parallel, it loses the ability to detect duplicated code
across modules. Duplicated code is usually a bad thing, so give pylint the
opportunity to let us know.

This makes pylint slightly slower, but going from 2 threads to 1 does not
make it anywhere close to twice as slow. On my machine, with Python 3.5,
pylint -j2 takes about 12s while single-threaded pylint takes about 16s
of wall clock time.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

tests/scripts/check-python-files.sh

@@ -67,7 +67,7 @@ elif [ "$1" = "--can-mypy" ]; then
 fi
 
 echo 'Running pylint ...'
-$PYTHON -m pylint -j 2 scripts/mbedtls_dev/*.py scripts/*.py tests/scripts/*.py || {
+$PYTHON -m pylint scripts/mbedtls_dev/*.py scripts/*.py tests/scripts/*.py || {
     echo >&2 "pylint reported errors"
     ret=1
 }