[VOL-5051] - Triage bbsim build

[VOL-5092] - verify_bbsim_unit-test repository failures in jenkins job history.

makefiles/*
-----------
  o Merge in latest library makefiles.
  o Some legacy retained:
      tools.mk => makefiles/docker/include.mk
      makefiles/lint/docker/*.mk (replace with docker/include.mk.new)

Makefile
--------
  o Remove bogus foobar target.
  o Target docs-lint now maps to library target lint-doc8.

docs/Makefile
-------------
  o venv install now handled by makefiles/virtualenv.mk
  o Replaced inlined doc8 lint target with makefiles/lint/doc8 (lint-doc8)
  o Use std defines for SHELL= and other constants.
  o Replace separator ';' with '&&' in commands using venv (detect errors).

config.mk
---------
  o Enable lint targets for doc8, docker & json.
  o More lint checks can be enabled but cleanup is needed first.

docs/Makefile
requirements.txt
----------------
  o Identified a few python module problems documented in VOL-5092.
  o Makefile wild target(%) matching stray dependencies so hardcode sphinx targets to act on.
  o Added hyphen/success to "make docs" until VOL-5092 can be straightened out.

Change-Id: Ibe4006747ee610bfe8ac0fdbb339e5e18e6e9176
diff --git a/makefiles/lint/python/flake8.mk b/makefiles/lint/python/flake8.mk
new file mode 100644
index 0000000..4d7ba93
--- /dev/null
+++ b/makefiles/lint/python/flake8.mk
@@ -0,0 +1,49 @@
+# -*- makefile -*-
+# -----------------------------------------------------------------------
+# Copyright 2022-2023 Open Networking Foundation (ONF) and the ONF Contributors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# 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.
+# -----------------------------------------------------------------------
+
+##-------------------##
+##---]  GLOBALS  [---##
+##-------------------##
+
+# Gather sources to check
+# TODO: implement deps, only check modified files
+python-check-find := find . -name '*venv*' -prune\
+  -o \( -name '*.py' \)\
+  -type f -print0
+
+##-------------------##
+##---]  TARGETS  [---##
+##-------------------##
+ifndef NO-LINT-PYTHON-FLAKE8
+  lint        : lint-python-flake8
+  lint-python : lint-python-flake8
+endif
+
+## -----------------------------------------------------------------------
+## Intent: Perform a lint check on makefile sources
+## -----------------------------------------------------------------------
+lint-python-flake8:
+	$(HIDE)$(env-clean) $(python-check-find) \
+	    | $(xargs-n1) flake8 --max-line-length=99 --count
+
+## -----------------------------------------------------------------------
+## Intent: Display command help
+## -----------------------------------------------------------------------
+help-summary ::
+	@echo '  lint-python-flake8  Syntax check python sources (*.py)'
+
+# [EOF]