Cluster: CLUSTER BUMPEPOCH introduced to help redis-trib fix.

Sometimes during "fixes" we have to setup a new configuration and assign
slots to nodes. With BUMPEPOCH we can make sure the new configuration of
the node will win if there are conflicting configurations (for example
another node is *also* claiming the same slot because the cluster is
totally messed up).

src/cluster.c

@@ -4022,6 +4022,13 @@ void clusterCommand(client *c) {
             }
             clusterDelSlot(slot);
             clusterAddSlot(n,slot);
+        } else if (!strcasecmp(c->argv[3]->ptr,"bumpepoch") && c->argc == 2) {
+            /* CLUSTER BUMPEPOCH */
+            int retval = clusterBumpConfigEpochWithoutConsensus();
+            sds reply = sdscatprintf(sdsempty(),"%s %llu\r\n",
+                    (retval == C_OK) ? "BUMPED" : "STILL",
+                    (unsigned long long) myself->configEpoch);
+            addReplySds(c,reply);
         } else {
             addReplyError(c,
                 "Invalid CLUSTER SETSLOT action or number of arguments");