BUG/MINOR: pools: use %u not %d to report pool stats in "show pools"

BUG/MINOR: pools: use %u not %d to report pool stats in "show pools"

In dump_pools_to_trash() we happen to use %d to display unsigned ints!

This has probably been there since "show pools" was introduced so this
fix must be backported to all versions. The impact is negligible since
no pool uses 2 billion entries. It could possibly affect the report of
failed allocation counts but in this case there's a bigger problem to
solved!

(cherry picked from commit cece694bcca10ec4d81346131297e66e35477dca)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>