rpc: increase server_test timeout

These timeouts are breaking tests in very slow
systems every once in a while.  I've noticed
problems when compiling the Ubuntu packages for
arm, specifically.

R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/4291058

src/pkg/rpc/server_test.go

@@ -312,12 +312,12 @@ func (WriteFailCodec) WriteRequest(*Request, interface{}) os.Error {
 }
 
 func (WriteFailCodec) ReadResponseHeader(*Response) os.Error {
-	time.Sleep(60e9)
+	time.Sleep(120e9)
 	panic("unreachable")
 }
 
 func (WriteFailCodec) ReadResponseBody(interface{}) os.Error {
-	time.Sleep(60e9)
+	time.Sleep(120e9)
 	panic("unreachable")
 }