build: clean up make help output

This change is designed to help the uninformed find the right way
to run extended tests by using the test-all[-debug] targets.
'make test EXTENDED_TESTS=y' fails to build as it has a dependency
on 'vom-install' which is conveniently included in test-all[-debug].

- clarify test-all[-debug] description and
  make test-help description
- Also align indentation of make help output

Type: style

Signed-off-by: Dave Wallace <dwallacelf@gmail.com>
Change-Id: Ief54cc8a5af68c052aacb0d660237c5eb63451b5