etcdserver: add timeout param on getClusterFromRemotePeers

It sets 10s timeout for public GetClusterFromRemotePeers.

This helps the following cases to work well in high latency scenario:

1. proxy sync members from the cluster
2. newly-joined member sync members from the cluster

Besides 10s request timeout, the request is also controlled by dial
timeout and read connection timeout.

etcdserver/cluster_util.go

@@ -30,7 +30,7 @@ import (
 // isMemberBootstrapped tries to check if the given member has been bootstrapped
 // in the given cluster.
 func isMemberBootstrapped(cl *cluster, member string, tr *http.Transport) bool {
-	rcl, err := getClusterFromRemotePeers(getRemotePeerURLs(cl, member), false, tr)
+	rcl, err := getClusterFromRemotePeers(getRemotePeerURLs(cl, member), time.Second, false, tr)
 	if err != nil {
 		return false
 	}
@@ -50,15 +50,17 @@ func isMemberBootstrapped(cl *cluster, member string, tr *http.Transport) bool {
 // these URLs. The first URL to provide a response is used. If no URLs provide
 // a response, or a Cluster cannot be successfully created from a received
 // response, an error is returned.
+// Each request has a 10-second timeout. Because the upper limit of TTL is 5s,
+// 10 second is enough for building connection and finishing request.
 func GetClusterFromRemotePeers(urls []string, tr *http.Transport) (*cluster, error) {
-	return getClusterFromRemotePeers(urls, true, tr)
+	return getClusterFromRemotePeers(urls, 10*time.Second, true, tr)
 }
 
 // If logerr is true, it prints out more error messages.
-func getClusterFromRemotePeers(urls []string, logerr bool, tr *http.Transport) (*cluster, error) {
+func getClusterFromRemotePeers(urls []string, timeout time.Duration, logerr bool, tr *http.Transport) (*cluster, error) {
 	cc := &http.Client{
 		Transport: tr,
-		Timeout:   time.Second,
+		Timeout:   timeout,
 	}
 	for _, u := range urls {
 		resp, err := cc.Get(u + "/members")