rbutil uses several components from the utils folder, and can be
considered part of utils too. Having it in a separate folder is an
arbitrary split that doesn't help anymore these days, so merge them.
This also allows other utils to easily use libtools.make without the
need to navigate to a different folder.
Change-Id: I3fc2f4de19e3e776553efb5dea5f779dfec0dc21
c876d3bbef