In order to try to avoid problems with leaking memory, context bleeding
from one layer to another, and lay the groundwork for supporting
updating all branches in one operation, split the updating of a single
layer out to its own internal script. This means that the tinfoil
instantiation and metadata parsing is in a completely separate process
per layer.
Implements [YOCTO #9647].
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
