Move the TryReusingBlob implementation
Move the TryReusingBlob implementation

... so that tryReusingBlobAsPending and
tryReusingBlobLocked are consecutive.  We will merge the two
(and TryReusingBlob will go away completley, eventually).

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

containers/image,containers/image