Don't use named return values in layerStore.Put
Don't use named return values in layerStore.Put

We will need want to refer to "layer" in a defer
block, in order to delete that layer. That doesn't work
with "layer" being a named return value, because a
(return nil, -1, ...) sets "layer" to nil.

So, turn "layer" into a local variable, and use an unnamed
return value. And beause all return values must be named,
or unnamed, consistently, turn "size" and "err" also into
local variables.

Then decrease the scope of the "size" and "err" local variables
to simplify understanding the code a bit.

Signed-off-by: Miloslav Trmač <9c008e38982a5397deb855345fb164f0558459ae@redhat.com>

containers/storage,containers/storage,containers/storage