of: unittest: overlay: Keep track of created overlays
of: unittest: overlay: Keep track of created overlays

During the course of the overlay selftests some of them remain
applied. While this does not pose a real problem, make sure you track
them and destroy them at the end of the test.

Signed-off-by: Pantelis Antoniou <4024101abe0c2bf4e288a39b760ad0c2158118b1@konsulko.com>
Signed-off-by: Rob Herring <fbb37eacae100e13076d5c4b46f06cfa4d6fa9f8@kernel.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs