Another attempt to deflake TestPullFromCentralRegistryImplicitRefParts

Retries after v1 fallbacks were added in moby#20411. The test still appears
to be flaky. There are two potential problems. The initial pull was not
protected against pulling from v1, so it could be giving us a different
hello-world image to compare against. Also, after experiencing a v1
fallback, we need to restore the original image before doing the next
pull, because otherwise the "Image is up to date for hello-world:latest"
message will not show up as expected.

See moby#17214.

Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>

integration-cli/docker_cli_pull_test.go

@@ -74,18 +74,10 @@ func (s *DockerHubPullSuite) TestPullNonExistingImage(c *check.C) {
 // multiple images.
 func (s *DockerHubPullSuite) TestPullFromCentralRegistryImplicitRefParts(c *check.C) {
 	testRequires(c, DaemonIsLinux)
-	s.Cmd(c, "pull", "hello-world")
-	defer deleteImages("hello-world")
 
-	for _, i := range []string{
-		"hello-world",
-		"hello-world:latest",
-		"library/hello-world",
-		"library/hello-world:latest",
-		"docker.io/library/hello-world",
-		"index.docker.io/library/hello-world",
-	} {
-		out := s.Cmd(c, "pull", i)
+	// Pull hello-world from v2
+	pullFromV2 := func(ref string) (int, string) {
+		out := s.Cmd(c, "pull", "hello-world")
 		v1Retries := 0
 		for strings.Contains(out, "this image was pulled from a legacy registry") {
 			// Some network errors may cause fallbacks to the v1
@@ -95,17 +87,51 @@ func (s *DockerHubPullSuite) TestPullFromCentralRegistryImplicitRefParts(c *chec
 			// few retries if we end up with a v1 pull.
 
 			if v1Retries > 2 {
-				c.Fatalf("too many v1 fallback incidents when pulling %s", i)
+				c.Fatalf("too many v1 fallback incidents when pulling %s", ref)
 			}
 
-			s.Cmd(c, "rmi", i)
-			out = s.Cmd(c, "pull", i)
+			s.Cmd(c, "rmi", ref)
+			out = s.Cmd(c, "pull", ref)
 
 			v1Retries++
 		}
+
+		return v1Retries, out
+	}
+
+	pullFromV2("hello-world")
+	defer deleteImages("hello-world")
+
+	s.Cmd(c, "tag", "hello-world", "hello-world-backup")
+
+	for _, ref := range []string{
+		"hello-world",
+		"hello-world:latest",
+		"library/hello-world",
+		"library/hello-world:latest",
+		"docker.io/library/hello-world",
+		"index.docker.io/library/hello-world",
+	} {
+		var out string
+		for {
+			var v1Retries int
+			v1Retries, out = pullFromV2(ref)
+
+			// Keep repeating the test case until we don't hit a v1
+			// fallback case. We won't get the right "Image is up
+			// to date" message if the local image was replaced
+			// with one pulled from v1.
+			if v1Retries == 0 {
+				break
+			}
+			s.Cmd(c, "rmi", ref)
+			s.Cmd(c, "tag", "hello-world-backup", "hello-world")
+		}
 		c.Assert(out, checker.Contains, "Image is up to date for hello-world:latest")
 	}
 
+	s.Cmd(c, "rmi", "hello-world-backup")
+
 	// We should have a single entry in images.
 	img := strings.TrimSpace(s.Cmd(c, "images"))
 	splitImg := strings.Split(img, "\n")