vitastor-cli: add commands to control pools: pool-create, pool-ls, pool-modify, pool-rm

PR #59 - https://github.com/vitalif/vitastor/pull/58/commits

By MIND Software LLC

By submitting this pull request, I accept Vitastor CLA

src/cli_merge.cpp

@@ -342,7 +342,11 @@ struct snap_merger_t
             printf("\rOverwriting blocks: %ju/%ju\n", to_process, to_process);
         }
         // Done
-        result = (cli_result_t){ .text = "Done, layers from "+from_name+" to "+to_name+" merged into "+target_name };
+        result = (cli_result_t){ .text = "Done, layers from "+from_name+" to "+to_name+" merged into "+target_name, .data = json11::Json::object {
+            { "from", from_name },
+            { "to", to_name },
+            { "into", target_name },
+        }};
         state = 100;
     resume_100:
         return;