build: fix make test with distributed src

This patch addresses the functionality that is
missing for distributed make test source files.
In addition it extends the concept of colocating
test source code with functional source code
(eg. src/vcl/test). It also cleans up deficiencies
in the make test makefiles.

NOTE: Due to the way sphinx document tools work,
all test, all of the make test python code is
gathered using soft links into the directory:
.../build-root/build-test/src

Change summary:
- Remove 'make test' help details from
  main makefile help output to reduce clutter
  and redundant help output
- Move all generated build output to
  .../build-root/build-test
- Move test_vcl.py as first usecase for
  distributed core feature make test code
- Add test-wipe-all target and fix wipe targets
  to remove all generated files
- Fix 'make test-doc' to generate module
  documentation for all source files
- Remove unused targets in test/doc/Makefile
- Fix 'make test-shell'
- Fix test/ext Makefile to not generate
  bogus output

Type: fix
Fixes: a43c93f8554ad7418e31be3791b3fb71232f60ac

Change-Id: Icc2ddb81d474081c3ede4548ecd7a0624651f62d
Signed-off-by: Dave Wallace <dwallacelf@gmail.com>