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/lint/yaml/find_utils.mk b/makefiles/lint/yaml/find_utils.mk
new file mode 100644
index 0000000..49d4cb0
--- /dev/null
+++ b/makefiles/lint/yaml/find_utils.mk
@@ -0,0 +1,32 @@
+# -*- makefile -*-
+# -----------------------------------------------------------------------
+# Intent:
+#   o Construct a find command able to gather python files with filtering.
+#   o Used by library makefiles flake8.mk and pylint.mk for iteration.
+# -----------------------------------------------------------------------
+
+## -----------------------------------------------------------------------
+## Intent: Construct a string for invoking find \( excl-pattern \) -prune
+# -----------------------------------------------------------------------
+gen-yaml-find-excl = \
+  $(strip \
+	-name '__ignored__' \
+	$(foreach dir,$($(1)),-o -name $(dir)) \
+  )
+
+## -----------------------------------------------------------------------
+## Intent: Construct a find command to gather a list of python files
+##         with exclusions.
+## -----------------------------------------------------------------------
+## Usage:
+#	$(activate) & $(call gen-python-find-cmd) | $(args-n1) pylint
+## -----------------------------------------------------------------------
+gen-yaml-find-cmd = \
+  $(strip \
+    find . \
+      \( $(call gen-yaml-find-excl,onf-excl-dirs) \) -prune \
+      -o \( -iname '*.yaml' -o -iname '*.yml' \) \
+      -print0 \
+  )
+
+# [EOF]