Writes and verify image

clitools/pkg/controller/osimage/helpers.go

@@ -0,0 +1,15 @@
+package osimage
+
+func PercentOf(done, total int64) int64 {
+	if total <= 0 {
+		return 0
+	}
+	p := (done * 100) / total
+	if p < 0 {
+		return 0
+	}
+	if p > 100 {
+		return 100
+	}
+	return p
+}