Multiclient E2E With Lighthouse (#10020)

* save work

* current progress

* fix it more

* save progress

* fixes so far

* add signature test

* fix up changes so far

* change to latest

* update lighthouse version

* fix build

* fix again

* do one

* clean up

* fix build

* fix it

* fix test

* change tag

* remove e2e

* Update config/params/testnet_e2e_config.go

Co-authored-by: Radosław Kapka <rkapka@wp.pl>

* update

* Update sha

Co-authored-by: Radosław Kapka <rkapka@wp.pl>
Co-authored-by: Raul Jordan <raul@prysmaticlabs.com>
Co-authored-by: prestonvanloon <preston@prysmaticlabs.com>

testing/endtoend/helpers/helpers.go

@@ -95,6 +95,53 @@ func WaitForTextInFile(file *os.File, text string) error {
 	}
 }
 
+// FindFollowingTextInFile checks a file every polling interval for the  following text requested.
+func FindFollowingTextInFile(file *os.File, text string) (string, error) {
+	d := time.Now().Add(maxPollingWaitTime)
+	ctx, cancel := context.WithDeadline(context.Background(), d)
+	defer cancel()
+
+	// Use a ticker with a deadline to poll a given file.
+	ticker := time.NewTicker(filePollingInterval)
+	defer ticker.Stop()
+	for {
+		select {
+		case <-ctx.Done():
+			contents, err := ioutil.ReadAll(file)
+			if err != nil {
+				return "", err
+			}
+			return "", fmt.Errorf("could not find requested text \"%s\" in logs:\n%s", text, contents)
+		case <-ticker.C:
+			fileScanner := bufio.NewScanner(file)
+			buf := make([]byte, 0, fileBufferSize)
+			fileScanner.Buffer(buf, maxFileBufferSize)
+			for fileScanner.Scan() {
+				scanned := fileScanner.Text()
+				if strings.Contains(scanned, text) {
+					lastIdx := strings.LastIndex(scanned, text)
+					truncatedIdx := lastIdx + len(text)
+					if len(scanned) <= truncatedIdx {
+						return "", fmt.Errorf("truncated index is larger than the size of whole scanned line")
+					}
+					splitObjs := strings.Split(scanned[truncatedIdx:], " ")
+					if len(splitObjs) == 0 {
+						return "", fmt.Errorf("0 split substrings retrieved")
+					}
+					return splitObjs[0], nil
+				}
+			}
+			if err := fileScanner.Err(); err != nil {
+				return "", err
+			}
+			_, err := file.Seek(0, io.SeekStart)
+			if err != nil {
+				return "", err
+			}
+		}
+	}
+}
+
 // GraffitiYamlFile outputs graffiti YAML file into a testing directory.
 func GraffitiYamlFile(testDir string) (string, error) {
 	b := []byte(`default: "Rice"