repart: Don't look for --make-ddi= definitions inside --root=

repart: Don't look for --make-ddi= definitions inside --root=

It doesn't really make sense to go looking for these inside the
given root directory. While we should resolve specifiers and such
based on the given root directory, let's look up the image definitions
on the host system as there's a good chance they're coupled to the
repart version we're using so there's all kinds of chances for problems
if we use the definitions from the image we're building instead of those
from the host.