VOL-4977 - Failure in voltha-protos verification job.

Makefile
makefiles/consts.mk
makefiles/include.mk
virtualenv.mk
requirements.txt
--------------------
  o Added library makefiles from repo:onf-make to handle virtualenv setup/removal.
  o go-clean - augment clean rule, current behavior leaves directory unbuildable.

makefiles/docker/include.mk
---------------------------
  o Replace inlined copies of docker cli arguments with macros: is-stdin, docker-run, etc.
  o Moved docker command wrappers: PROTOC, etc into docker/include.mk

makefiles/help/*.mk
-------------------
  o Update and align makefile target help text.

Change-Id: Ifcf72e8081efc6e0d828ee4b1b96c66a219a39b9
15 files changed