platformutil: add local platform

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

util/platformutil/parse.go

@@ -22,7 +22,7 @@ func Parse(platformsStr []string) ([]specs.Platform, error) {
 			out = append(out, p...)
 			continue
 		}
-		p, err := platforms.Parse(s)
+		p, err := parse(s)
 		if err != nil {
 			return nil, err
 		}
@@ -31,6 +31,13 @@ func Parse(platformsStr []string) ([]specs.Platform, error) {
 	return out, nil
 }
 
+func parse(in string) (specs.Platform, error) {
+	if strings.EqualFold(in, "local") {
+		return platforms.DefaultSpec(), nil
+	}
+	return platforms.Parse(in)
+}
+
 func Dedupe(in []specs.Platform) []specs.Platform {
 	m := map[string]struct{}{}
 	out := make([]specs.Platform, 0, len(in))