Fix generating random object IDs
Fix generating random object IDs

If callers to Store don't provide container/image/layer
IDs, Store generates random values without checking
for collisions.

Meanwhile, the underlying per-object stores do check for
collisions, which is more reliable, and nothing in
Store needs to know the values in advance (any more), so
just delete the code that generates the random values,
exposing the better per-object ID generation code.

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

containers/storage,containers/storage,containers/storage