Sequantially garbage collect on peers

IPFS garbage collection stops add and remove, so running garbage
collection on all nodes at once would cause many cluster functionalities
to error
Do it sequantially to avoid that problem.

cluster.go

@@ -1895,42 +1895,34 @@ func (c *Cluster) RepoGC(ctx context.Context) (*api.GlobalRepoGC, error) {
 		logger.Error(err)
 		return nil, err
 	}
-	lenMembers := len(members)
 
-	ctxs, cancels := rpcutil.CtxsWithCancel(ctx, lenMembers)
-	defer rpcutil.MultiCancel(cancels)
-
-	repoGCsResp := make([]*api.RepoGC, lenMembers, lenMembers)
-
-	errs := c.rpcClient.MultiCall(
-		ctxs,
-		members,
-		"Cluster",
-		"RepoGCLocal",
-		struct{}{},
-		rpcutil.CopyRepoGCSliceToIfaces(repoGCsResp),
-	)
-
-	// clubbing `RepoGCLocal` responses of all peers into one
+	// to club `RepoGCLocal` responses of all peers into one
 	globalRepoGC := api.GlobalRepoGC{PeerMap: make(map[string]*api.RepoGC)}
-	for i, resp := range repoGCsResp {
-		e := errs[i]
-
-		if e == nil {
-			globalRepoGC.PeerMap[peer.IDB58Encode(members[i])] = resp
+	for _, member := range members {
+		var repoGC api.RepoGC
+		err = c.rpcClient.CallContext(
+			ctx,
+			member,
+			"Cluster",
+			"RepoGCLocal",
+			struct{}{},
+			&repoGC,
+		)
+		if err == nil {
+			globalRepoGC.PeerMap[peer.IDB58Encode(member)] = &repoGC
 			continue
 		}
 
-		if rpc.IsAuthorizationError(e) {
-			logger.Debug("rpc auth error:", e)
+		if rpc.IsAuthorizationError(err) {
+			logger.Debug("rpc auth error:", err)
 			continue
 		}
 
-		logger.Errorf("%s: error in broadcast response from %s: %s ", c.id, members[i], e)
+		logger.Errorf("%s: error in broadcast response from %s: %s ", c.id, member, err)
 
-		globalRepoGC.PeerMap[peer.IDB58Encode(members[i])] = &api.RepoGC{
-			Peer:     members[i],
-			Peername: peer.IDB58Encode(members[i]),
+		globalRepoGC.PeerMap[peer.IDB58Encode(member)] = &api.RepoGC{
+			Peer:     member,
+			Peername: peer.IDB58Encode(member),
 			Keys:     []api.IPFSRepoGC{},
 			Error:    err.Error(),
 		}