Fix a couple of instances where += is used with a variable :append
definition, this future-proofs for Kirkstone (it currently triggers
a warning on poky master, as may soon be treated as an error).
Bug-AGL: SPEC-3819
Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: I1ff076e174d686226dc4507413ec11dcda2e77db