makefiles/
----------
  o Adding more lint target logic.
  o Copy in virtualenv.mk from voltha-docs to support dependency
    based virtualenv installations.

*/*.yaml
--------
  o Misc yamllint cleanups.

Makefile
--------
  o Prune inlined logic since replaced by library makefile logic.
  o Replaced explicit pyenv installation with dependency driven
    so venv will only require installation once per target run.
  o Library make clean/sterile targets handle cleanup.

Change-Id: Ie2ce0ebc01b07c0004a5904c2641c394e46d5044
diff --git a/makefiles/lint/robot.mk b/makefiles/lint/robot.mk
index 1c7119f..f33c4ba 100644
--- a/makefiles/lint/robot.mk
+++ b/makefiles/lint/robot.mk
@@ -28,7 +28,9 @@
 
 .PHONY: lint-robot
 
-lint : lint-robot
+ifndef NO-LINT-ROBOT
+  lint : lint-robot
+endif
 
 lint-robot: vst_venv
 	source ./$</bin/activate \