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/help/include.mk b/makefiles/help/include.mk
index f8200a7..a3a1320 100644
--- a/makefiles/help/include.mk
+++ b/makefiles/help/include.mk
@@ -1,6 +1,6 @@
 # -*- makefile -*-
 # -----------------------------------------------------------------------
-# Copyright 2017-2023 Open Networking Foundation (ONF) and the ONF Contributors
+# Copyright 2017-2022 Open Networking Foundation
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -15,9 +15,32 @@
 # limitations under the License.
 # -----------------------------------------------------------------------
 
-include $(MAKEDIR)/help/go.mk
-include $(MAKEDIR)/help/python.mk
-include $(MAKEDIR)/help/java.mk
-include $(MAKEDIR)/help/clean.mk
+# Parent makefile should include this early so help
+# message will be prefixed by a usage statement.
+help ::
+	@echo "Usage: $(MAKE) [options] [target] ..."
+	@echo
+	@echo '[Virtual Env]'
+	@echo '  venv           Create a python virtual environment'
+	@echo '  venv_protos    Create a python virtual environment'
+	@echo "  $(VENV_NAME)"
+	@echo
+	@echo '[ACTION] - golang, java and python'
+	@echo '  protos'
+	@echo '  build'
+	@echo '  test'
+	@echo
+	@echo '[CLEAN]'
+	@echo '  clean          Remove generated targets'
+	@echo '  sterile        clean + remove virtual env interpreter install'
+	@echo
+	@echo '[HELP]'
+	@echo '  help           Display program help'
+#	@echo '  help-verbose   Display additional targets and help'
+	@echo
+	@echo '[PROTOS: generate]'
+	@echo '  go-protos'
+	@echo '  java-protos'
+	@echo '  python-protos'
 
 # [EOF]
diff --git a/makefiles/help/variables.mk b/makefiles/help/variables.mk
new file mode 100644
index 0000000..a50b233
--- /dev/null
+++ b/makefiles/help/variables.mk
@@ -0,0 +1,36 @@
+# -*- makefile -*-
+# -----------------------------------------------------------------------
+# Copyright 2017-2022 Open Networking Foundation
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# -----------------------------------------------------------------------
+
+# Include variables.mk after library makefiles have been included
+
+ifdef VERBOSE
+  help :: help-variables
+else
+  help ::
+	@echo
+	@echo '[VARIABLES] - Conditional makefile behavior'
+	@echo '  see also: help-variables'
+endif
+
+help-variables:
+	@echo
+	@echo '[VARIABLES] - Conditional makefile behavior'
+	@echo '  NO_PATCHES=           Do not apply patches to the python virtualenv'
+	@echo '  NO_OTHER_REPO_DOCS=   No foreign repos, only apply target to local sources.'
+	@echo '  VERBOSE=              Display extended help'
+
+# [EOF]