kunit: tool: add --kernel_args to allow setting module params

kunit.py currently does not make it possible for users to specify module
parameters (/kernel arguments more generally) unless one directly tweaks
the kunit.py code itself.

This hasn't mattered much so far, but this would make it easier to port
existing tests that expose module parameters over to KUnit and/or let
current KUnit tests take advantage of them.

Tested using an kunit internal parameter:
$ ./tools/testing/kunit/kunit.py run --kunitconfig=lib/kunit \
    --kernel_args=kunit.filter_glob=kunit_status
...
Testing complete. 2 tests run. 0 failed. 0 crashed. 0 skipped.

Signed-off-by: Daniel Latypov <dlatypov@google.com>
Reviewed-by: David Gow <davidgow@google.com>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>