registration: Fix merging of array_plus

We want the local configuration ($GLOBALS[$key]) to override the default
values ($val). This matches what array_merge does.

Bug: T112868
Change-Id: I9c333a1fa67d3f24e09ffed3072b2897389f6139
(cherry picked from commit 0a83ef3cf765385691a099dbb85e283b43dc5465)