Force python3 pylint

Some distributions provide python2 version of pylint package by default,
but all provide pylint for python3 in some package.  Python 2 reaches
EOL in few months, so there's no reason to support it.

This prevents our scripts from being accidentally marked invalid due to
language changes between python 2 and 3.  Also, newer pylint has nicer
output, that provides exact module filename straight in the warning.

scripts/verify-python.sh

@@ -7,6 +7,11 @@
 # the repo.  You can pass additional parameters to this script itself, e.g.:
 #
 # $ ./verify-python.sh --disable=<msg_ids>
+#
+# This script uses exclusively python3 version of pylint; most distributions
+# provide it in a package pylint, but some call it pylint3 or python3-pylint.
+
+set -e
 
 list_python_files () {
 	git ls-files \
@@ -16,11 +21,13 @@ list_python_files () {
 }
 
 main () {
-	pylint --version >&2
+	# Using "python3 -m pylint" to avoid using python2-only
+	# version of pylint by mistake.
+	python3 -m pylint --version >&2
 	echo "Checking files:" >&2
 	list_python_files >&2
 	local -r rc="$(git rev-parse --show-toplevel)/.pylint"
-	list_python_files | xargs -L 1000 pylint --rcfile="$rc" "$@"
+	list_python_files | xargs -L 1000 python3 -m pylint --rcfile="$rc" "$@"
 }
 
 main "$@"