Fix issues with the URE unorc in the MACLIKE_APP_STRUCTURE case

Not sure it it is cleaner to use relative paths from ${ORIGIN}, or
paths below ${BRAND_BASE_DIR}. Now I use the former in the URE unorc
constructed in scp2, and the latter in the one expanded from
ure/source/unorc.in. (Whether these two really need to be separate or
not, no idea. Historical reasons? Different use cases, unit tests and
actual end-user install tree?)

Change-Id: Ib5f11176de1d5d983cac8358d67788ebc20f2b13