testing,internal/fuzz: Whether to support printing random corpus in the future

[gcggcg]

###Whether to support printing random corpus in the future, so that we can check which data has been tested .Since I found that the Print didn't work even if I added fmt.Print, I wanted an error-like interrupt to Print out what I wanted to Print.

[heschi]

cc @golang/fuzzing

[c-seeger]

was trying to use fmt.Sprintf to construct the input string for the function to test until I realised i can't use fmt.
e.g.

f.Add("test")
f.Fuzz(func(t *testing.T), s string) {
  s := fmt.Sprintf("...%s", s)
  FuncToFuzz(s)
}