make error log more verbose

[rongyi]

in this file: skynetservices/skydns/server/forwarding.go:61

logf("failure to forward request %q", err)
an example log is like this:
I0518 07:20:37.179766 1 logs.go:41] skydns: failure to forward request "read udp xx.xx.xx.xx:28188->xx.xx.xx.xx:53: i/o timeout"
can we add question string (domain) string here ? so we can debug effectively