config: check and correct format of addr and URL

[lance6716]

What problem does this PR solve?

check and correct format of addr and URL in config files

What is changed and how it works?

for xxx-addr, it should not have a scheme. for xxx-urls and its parent config, such as join, initial-cluster, element in it should have a scheme

Check List

Tests

• Unit test
• Integration test

Code changes

• Has exported function/method change

Side effects

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation [https://github.com/zh: update join config docs-dm#303]

[csuzhangxc]

CI failed

[lance6716]

CI failed

will check testMaster.TestServer soon

[csuzhangxc]

LGTM

[lance6716]

seems gRPC (at lease our specified version) should remove http://, otherwise it can't connect

package main

import (
	"context"
	"log"
	"net"
	"time"

	"google.golang.org/grpc"
)

func main() {
	go func() {
		port := "127.0.0.1:8261"
		lis, err := net.Listen("tcp", port)
		if err != nil {
			log.Fatalf("failed to listen: %v", err)
		}
		s := grpc.NewServer()

		if err := s.Serve(lis); err != nil {
			log.Fatalf("failed to serve: %v", err)
		}
	}()

	time.Sleep(time.Second)
	ctx1, cancel1 := context.WithTimeout(context.Background(), 3*time.Second)
	conn, err := grpc.DialContext(ctx1, "http://127.0.0.1:8261", grpc.WithInsecure(), grpc.WithBlock(), grpc.WithBackoffMaxDelay(3*time.Second))
	if err != nil {
		log.Fatalf("did not connect: %v", err)
	}
	defer conn.Close()
	cancel1()
}

[GMHDBJD]

LGTM

[ti-srebot]

cherry pick to release-2.0 in PR #955