packaging: build: handle multiple files in exclude of recursive copy

the output of find... contained mixed newline and space delimited file
list, workout find to return space delimited to avoid issues within
the target.

Change-Id: I4711908f398ff8f848b87017e47f37caecec5b2f
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>
Reported-By: Martin Perina <mperina@redhat.com>