Update etcd/README.md for multiple endpoints, and add additional test cases (#1277)

This fix tries to address the issue raised in 1275 to clarify
the syntax for multiple endpoints specification.

This fix also adds additional test cases to demo the usage.

This fix fixes 1275.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

plugin/etcd/README.md

@@ -79,6 +79,14 @@ when resolving external pointing CNAMEs.
 }
 ~~~
 
+Multiple endpoints are supported as well.
+
+~~~
+etcd skydns.local {
+    endpoint http://localhost:2379 http://localhost:4001
+...
+~~~
+
 
 ### Reverse zones
 

plugin/etcd/setup_test.go

@@ -12,25 +12,31 @@ func TestSetupEtcd(t *testing.T) {
 		input              string
 		shouldErr          bool
 		expectedPath       string
-		expectedEndpoint   string
+		expectedEndpoint   []string
 		expectedErrContent string // substring from the expected error. Empty for positive cases.
 	}{
 		// positive
 		{
-			`etcd`, false, "skydns", "http://localhost:2379", "",
+			`etcd`, false, "skydns", []string{"http://localhost:2379"}, "",
+		},
+		{
+			`etcd {
+	endpoint http://localhost:2379 http://localhost:3379 http://localhost:4379
+
+}`, false, "skydns", []string{"http://localhost:2379", "http://localhost:3379", "http://localhost:4379"}, "",
 		},
 		{
 			`etcd skydns.local {
 	endpoint localhost:300
 }
-`, false, "skydns", "localhost:300", "",
+`, false, "skydns", []string{"localhost:300"}, "",
 		},
 		// negative
 		{
 			`etcd {
 	endpoints localhost:300
 }
-`, true, "", "", "unknown property 'endpoints'",
+`, true, "", []string{""}, "unknown property 'endpoints'",
 		},
 	}
 
@@ -57,8 +63,15 @@ func TestSetupEtcd(t *testing.T) {
 		if !test.shouldErr && etcd.PathPrefix != test.expectedPath {
 			t.Errorf("Etcd not correctly set for input %s. Expected: %s, actual: %s", test.input, test.expectedPath, etcd.PathPrefix)
 		}
-		if !test.shouldErr && etcd.endpoints[0] != test.expectedEndpoint { // only checks the first
-			t.Errorf("Etcd not correctly set for input %s. Expected: '%s', actual: '%s'", test.input, test.expectedEndpoint, etcd.endpoints[0])
+		if !test.shouldErr {
+			if len(etcd.endpoints) != len(test.expectedEndpoint) {
+				t.Errorf("Etcd not correctly set for input %s. Expected: '%+v', actual: '%+v'", test.input, test.expectedEndpoint, etcd.endpoints)
+			}
+			for i, endpoint := range etcd.endpoints {
+				if endpoint != test.expectedEndpoint[i] {
+					t.Errorf("Etcd not correctly set for input %s. Expected: '%+v', actual: '%+v'", test.input, test.expectedEndpoint, etcd.endpoints)
+				}
+			}
 		}
 	}
 }