Makefile library merge with onf-make and voltha-lib-go

makefiles/
----------
  o Import standalone makefile directories to checkin smaller parts of a mega patch.
  o Build out directory hierarchy by topic and feature.

makefiles/lint/yaml/
--------------------
  o Pull in logic evolved in repo:voltha-lib-go.
  o Refactoring: support special snowflake targets by repository.
  o ci-management and voltha-lib-go use distinct yamllint.conf files.
  o Separate until there is time to review and consolidate.
  o Added deps for on-demand local install of yamllint.
    - requirements.txt could be used but every build would incur overhead.

Makefile
--------
  o Use latest syntax from repo:onf-make.
  o No need to set path variables, makefiles/include.mk can infer them.
  o Added a help target to explicitly display targets and suggestions.
  o Logic is bundled in libraries and use of 'make help' is not well known.

Change-Id: Id8eba6f914a7bfe9a31637901bd8fb78a387e0c2
diff --git a/makefiles/virtualenv.mk b/makefiles/virtualenv.mk
index 93eb29d..dae1ab8 100644
--- a/makefiles/virtualenv.mk
+++ b/makefiles/virtualenv.mk
@@ -13,7 +13,7 @@
 # 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.
-## -----------------------------------------------------------------------
+# -----------------------------------------------------------------------
 # https://gerrit.opencord.org/plugins/gitiles/onf-make
 # ONF.makefile.version = 1.0
 # -----------------------------------------------------------------------
@@ -30,8 +30,8 @@
 ##------------------##
 venv-name            ?= .venv#                            # default install directory
 venv-abs-path        := $(PWD)/$(venv-name)
-
-venv-activate-script := $(venv-name)/bin/activate#        # dependency
+venv-activate-bin    := $(venv-name)/bin
+venv-activate-script := $(venv-activate-bin)/activate#    # dependency
 
 # Intent: activate= is a macro for accessing the virtualenv activation script#
 #  Usage: $(activate) && python