Documentation: KUnit: avoid repeating "kunit.py run" in start.rst

Documentation: KUnit: avoid repeating "kunit.py run" in start.rst

Combine two sections mentioning "kunit.py run" to streamline the
getting-started guide. Update "kunit.py run" expected output in
the guide and run_wrapper.

Signed-off-by: Tales Aparecida <tales.aparecida@gmail.com>
Reviewed-by: Maíra Canal <mairacanal@riseup.net>
Reviewed-by: Sadiya Kazi<sadiyakazi@google.com>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>