net/rpc: skip TestGobError on Plan 9

LGTM=bradfitz
R=rsc, bradfitz
CC=aram, golang-codereviews
https://golang.org/cl/154140043

src/net/rpc/client_test.go

@@ -52,6 +52,9 @@ func (s *S) Recv(nul *struct{}, reply *R) error {
 }
 
 func TestGobError(t *testing.T) {
+	if runtime.GOOS == "plan9" {
+		t.Skip("skipping test; see http://golang.org/issue/8908")
+	}
 	defer func() {
 		err := recover()
 		if err == nil {