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/robot.mk b/makefiles/lint/robot.mk
index 9808602..ec5579e 100644
--- a/makefiles/lint/robot.mk
+++ b/makefiles/lint/robot.mk
@@ -32,8 +32,8 @@
 
 lint-robot: vst_venv
 	source ./$</bin/activate \
-	    && set -u \
-	    && rflint $(LINT_ARGS) $(ROBOT_FILES)
+	    ; set -u \
+	    ; rflint $(LINT_ARGS) $(ROBOT_FILES)
 
 help::
 	@echo "  lint-robot           Syntax check robot sources using rflint"