An attempt to fix distrib test

test/distrib/python/test_packages.sh

@@ -37,7 +37,7 @@ TESTING_ARCHIVES=("$EXTERNAL_GIT_ROOT"/input_artifacts/grpcio-testing-[0-9]*.tar
 VIRTUAL_ENV=$(mktemp -d)
 virtualenv "$VIRTUAL_ENV"
 PYTHON=$VIRTUAL_ENV/bin/python
-"$PYTHON" -m pip install --upgrade six pip
+"$PYTHON" -m pip install --upgrade six pip wheel
 
 function validate_wheel_hashes() {
   for file in "$@"; do