Fix crashes, print some stats

Notably:
- fix the `delete op` inside lambda callback crash (it frees the lambda itself
  which results in use-after-free with g++)
- fix stop_client() reenterability
- fix a bug in the blockstore layer which resulted in always returning version=0
  for zero-length reads
- change error codes for blockstore_stabilize

osd_peering_pg.cpp

@@ -204,6 +204,14 @@ void pg_obj_state_check_t::finish_object()
         {
             printf("Present on: osd %lu, role %ld%s\n", list[i].osd_num, (list[i].oid.stripe & STRIPE_MASK), list[i].is_stable ? " (stable)" : "");
         }
+        if (0)
+        {
+            // For future debug level
+            for (int i = obj_start; i < obj_end; i++)
+            {
+                printf("v%lu present on: osd %lu, role %ld%s\n", list[i].version, list[i].osd_num, (list[i].oid.stripe & STRIPE_MASK), list[i].is_stable ? " (stable)" : "");
+            }
+        }
         state = OBJ_INCOMPLETE;
         pg->state = pg->state | PG_HAS_INCOMPLETE;
     }