kola: support nightly version in version comparions

The nightly version is the build date but the build ID has the branch
reference. To support the version comparion for nightly builds we need
to generate a version for the "main" branch and the major version
branches that is higher than the current release version.

Use 9999.99.99 as version in the semantic version checks for nightly
builds from the "main" branch or custom dev builds and use MAJOR.99.99
as version for nightly builds from the release branch.

kola/harness.go

@@ -432,10 +432,25 @@ func getClusterSemver(flight platform.Flight, outputDir string) (*semver.Version
 
 	out, stderr, err := m.SSH("grep ^VERSION_ID= /etc/os-release")
 	if err != nil {
-		return nil, fmt.Errorf("parsing /etc/os-release: %v: %s", err, stderr)
+		return nil, fmt.Errorf("parsing /etc/os-release for VERSION_ID: %v: %s", err, stderr)
 	}
 	ver := strings.Split(string(out), "=")[1]
 
+	out, stderr, err = m.SSH("grep ^BUILD_ID= /etc/os-release | { grep -o 'dev-.*-nightly' || true ; } | cut -d - -f 2-  | rev | cut -d - -f 2- | rev")
+	if err != nil {
+		return nil, fmt.Errorf("parsing /etc/os-release for nightly branch in BUILD_ID: %v: %s", err, stderr)
+	}
+	branch := string(out)
+	if branch == "main" || branch == "flatcar-master" {
+		// "main" is a nightly build of the main branch,
+		// "flatcar-master" refers to the manifest branch where dev builds are started
+		ver = "9999.99.99"
+	} else if strings.HasPrefix(branch, "flatcar-") {
+		// flatcar-MAJOR is a nightly build of the release branch
+		major := strings.Split(branch, "-")[1]
+		ver = major + ".99.99"
+	}
+
 	// TODO: add distro specific version handling
 	switch Options.Distribution {
 	case "cl":