mirror clone: Improve handling of latest versions

1. If a version is specified and we fall back on the latest version
   then print a message about this.
2. Allow specifying "latest" as version to download the latest version
   of all components.

pkg/repository/clone_mirror.go

@@ -464,6 +464,9 @@ func combineVersions(versions *[]string,
 					if latest == "" {
 						continue
 					}
+					if selectedVersion != "latest" {
+						fmt.Printf("%s %s/%s %s not found, using %s instead.\n", manifest.ID, os, arch, selectedVersion, latest)
+					}
 					selectedVersion = latest
 				}
 				if !result.Exist(selectedVersion) {

pkg/utils/semver.go

@@ -22,6 +22,7 @@ import (
 
 // NightlyVersionAlias represents latest build of master branch.
 const NightlyVersionAlias = "nightly"
+const LatestVersionAlias = "latest"
 
 // FmtVer converts a version string to SemVer format, if the string is not a valid
 // SemVer and fails to parse and convert it, an error is raised.
@@ -33,6 +34,11 @@ func FmtVer(ver string) (string, error) {
 		return v, nil
 	}
 
+	// latest version is an alias
+	if strings.ToLower(v) == LatestVersionAlias {
+		return v, nil
+	}
+
 	if !strings.HasPrefix(ver, "v") {
 		v = fmt.Sprintf("v%s", ver)
 	}