Fix TestHttpsInsecure on Plan 9 (#254)

* Handle "listen hungup" error on Plan 9 in TestHttpsInsecure

Plan 9 returns the "listen hungup" error when closing a closed listener.

See https://github.com/0intro/plan9/blob/4225c3e/sys/src/9/ip/devip.c#L476

Fixes #253.

* Handle empty profile on Plan 9 in TestHttpsInsecure

CPU profiling isn't implemented on Plan 9.

See golang.org/issues/22564.

Fixes #253.

internal/driver/fetch_test.go

 	return c.Get("file:///" + file)
 }
 
+func closedError() string {
+	if runtime.GOOS == "plan9" {
+		return "listen hungup"
+	}
+	return "use of closed"
+}
+
 func TestHttpsInsecure(t *testing.T) {
 	if runtime.GOOS == "nacl" {
 		t.Skip("test assumes tcp available")
 		donec <- http.Serve(l, nil)
 	}(donec)
 	defer func() {
-		if got, want := <-donec, "use of closed"; !strings.Contains(got.Error(), want) {
+		if got, want := <-donec, closedError(); !strings.Contains(got.Error(), want) {
 			t.Fatalf("Serve got error %v, want %q", got, want)
 		}
 	}()
 	if len(p.SampleType) == 0 {
 		t.Fatalf("fetchProfiles(%s) got empty profile: len(p.SampleType)==0", address)
 	}
+	if runtime.GOOS == "plan9" {
+		// CPU profiling is not supported on Plan9; see golang.org/issues/22564.
+		return
+	}
 	if len(p.Function) == 0 {
 		t.Fatalf("fetchProfiles(%s) got non-symbolized profile: len(p.Function)==0", address)
 	}
 var badSigprofOS = map[string]bool{
 	"darwin": true,
 	"netbsd": true,
-	"plan9":  true,
 }
 
 func checkProfileHasFunction(p *profile.Profile, fname string) error {