ctlv3: ensure synced member list before printing env vars on member add

In cases of multiple endpoints, it's possible member add would get a its
member list from a member that has not yet recognized the membership
update. Instead, confirm that the member list response is from the
member that acked the member add or from a member that has synced
with the cluster following the member add.

Fixes #7498

etcdctl/ctlv3/command/member_command.go

@@ -107,7 +107,8 @@ func memberAddCommandFunc(cmd *cobra.Command, args []string) {
 
 	urls := strings.Split(memberPeerURLs, ",")
 	ctx, cancel := commandCtx(cmd)
-	resp, err := mustClientFromCmd(cmd).MemberAdd(ctx, urls)
+	cli := mustClientFromCmd(cmd)
+	resp, err := cli.MemberAdd(ctx, urls)
 	cancel()
 	if err != nil {
 		ExitWithError(ExitError, err)
@@ -118,12 +119,24 @@ func memberAddCommandFunc(cmd *cobra.Command, args []string) {
 
 	if _, ok := (display).(*simplePrinter); ok {
 		ctx, cancel = commandCtx(cmd)
-		listResp, err := mustClientFromCmd(cmd).MemberList(ctx)
-		cancel()
-
-		if err != nil {
-			ExitWithError(ExitError, err)
+		listResp, err := cli.MemberList(ctx)
+		// get latest member list; if there's failover new member might have outdated list
+		for {
+			if err != nil {
+				ExitWithError(ExitError, err)
+			}
+			if listResp.Header.MemberId == resp.Header.MemberId {
+				break
+			}
+			// quorum get to sync cluster list
+			gresp, gerr := cli.Get(ctx, "_")
+			if gerr != nil {
+				ExitWithError(ExitError, err)
+			}
+			resp.Header.MemberId = gresp.Header.MemberId
+			listResp, err = cli.MemberList(ctx)
 		}
+		cancel()
 
 		conf := []string{}
 		for _, memb := range listResp.Members {