Abbreviate too long filenames to show progress

When the prefix string gets too long, the cheggaaa/pb
progress bar library doesn't show the remaining time.

pkg/minikube/download/progressbar.go

@@ -48,6 +48,11 @@ func (cpb *progressBar) TrackProgress(src string, currentSize, totalSize int64,
 	}
 	p := pb.Full.Start64(totalSize)
 	fn := filepath.Base(src)
+	// abbreviate filename for progress
+	maxwidth := 30 - len("...")
+	if len(fn) > maxwidth {
+		fn = fn[0:maxwidth] + "..."
+	}
 	p.Set("prefix", "    > "+fn+": ")
 	p.SetCurrent(currentSize)
 	p.Set(pb.Bytes, true)