VOL-4836: VOLTHA release prep.

Makefile
--------
  o Update copyright notice.
  o include a few library makefiles for displaying help, etc.
  o Added target sterile to make clean + remove venv.
  o Replace inlined rm -fr, rm -f with make builtin $(RM) && $(RM) -r

tox.ini
-------
  o Add more interpreter versions to envlist so python 3.10.x can be used.

Change-Id: Ideb7e30ff703dff18b707226a4821455f5b1f261
diff --git a/makefiles/lint/python.mk b/makefiles/lint/python.mk
index 86503a7..5aecd58 100644
--- a/makefiles/lint/python.mk
+++ b/makefiles/lint/python.mk
@@ -21,11 +21,12 @@
 
 lint : lint-python
 
+# check deps for format and python3 cleanliness
 lint-python: vst_venv
-	-source ./$</bin/activate \
-	    && set -u \
-	    && pylint $(PYTHON_FILES) \
-	    && flake8 --max-line-length=99 --count $(PYTHON_FILES)
+	source ./$</bin/activate \
+	    ; set -u \
+	    ; pylint --py3k $(PYTHON_FILES) \
+	    ; flake8 --max-line-length=99 --count $(PYTHON_FILES)
 
 help::
 	@echo "  lint-python          Syntax check using pylint and flake8"