Rename vmlinuz image and initrd image to bypass making unnecessary grub2 menuentry.

When generating grub2 config file, it create menuentries for each /boot/vmlinuz-* file.
Since this test-framework make its grub entry by hand, it's unneccesary to make it twice.
Change config.base to add new filesystems and remove unnecessary drivers.
Rework tests running on guest.

Now we can set multiple tests at once in the config file.
remove unnecessary comments.
Add selftests test taget.

It runs selftest test suite in linux kernel itself.
Currently it's marked as EXPERIMENTAL since some of them fail
inappropriately due to bugs in both test-linux-stable and selftest
itself. I'll remove it later...