OCPBUGS-34953: analyze: improve error msg when gather fails

Give a better error message when the gather logs are not collected
rather than
```
time="2024-06-05T08:34:45-04:00" level=error msg="The bootstrap machine did not execute the release-image.service systemd unit"
```
The release-image service could have been executed but we don't know if
the installer cannot connect to the bootstrap node (e.g, in a private
install).

Author: r4f4

pkg/gather/service/analyze.go

@@ -44,6 +44,7 @@ func analyzeGatherBundle(bundleFile io.Reader) error {
 	// read through the tar for relevant files
 	tarReader := tar.NewReader(uncompressedStream)
 	serviceAnalyses := make(map[string]analysis)
+	servicesFound := make([]string, 0)
 	for {
 		header, err := tarReader.Next()
 		if err == io.EOF {
@@ -61,6 +62,7 @@ func analyzeGatherBundle(bundleFile io.Reader) error {
 			continue
 		}
 		serviceName := serviceEntriesFileSubmatch[1]
+		servicesFound = append(servicesFound, serviceName)
 
 		serviceAnalysis, err := analyzeService(tarReader)
 		if err != nil {
@@ -71,6 +73,11 @@ func analyzeGatherBundle(bundleFile io.Reader) error {
 		serviceAnalyses[serviceName] = serviceAnalysis
 	}
 
+	if len(servicesFound) == 0 {
+		logrus.Error("Invalid log bundle or the bootstrap machine could not be reached and bootstrap logs were not collected")
+		return nil
+	}
+
 	analysisChecks := []struct {
 		name     string
 		check    func(analysis) bool

pkg/gather/service/analyze_test.go

@@ -54,7 +54,7 @@ func TestAnalyzeGatherBundle(t *testing.T) {
 		{
 			name: "no files",
 			expectedOutput: []logrus.Entry{
-				{Level: logrus.ErrorLevel, Message: "The bootstrap machine did not execute the release-image.service systemd unit"},
+				{Level: logrus.ErrorLevel, Message: "Invalid log bundle or the bootstrap machine could not be reached and bootstrap logs were not collected"},
 			},
 		},
 		{