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/json.mk b/makefiles/lint/json.mk
index cc9ecfa..0a11c71 100644
--- a/makefiles/lint/json.mk
+++ b/makefiles/lint/json.mk
@@ -15,7 +15,7 @@
 # limitations under the License.
 # -----------------------------------------------------------------------
 
-JSON_FILES ?= $(error JSON_FILES= is required)
+JSON_FILES ?= $(error JSON_FILES= is rqeuired)
 
 .PHONY: lint-json