Documentation: kunit: Reorganize documentation related to running tests

Consolidate documentation running tests into two pages: "run tests with
kunit_tool" and "run tests without kunit_tool".

Signed-off-by: Harinder Singh <sharinder@google.com>
Reviewed-by: Tim Bird <tim.bird@sony.com>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Link: https://lore.kernel.org/r/20211217044911.798817-5-sharinder@google.com


Signed-off-by: Jonathan Corbet <corbet@lwn.net>