Lookup IP addresses properly.
Lookup IP addresses properly.

(Addr.String() includes the network suffix, which net.LookupAddr doesn't like)

BUG=541412

Review URL: https://codereview.chromium.org/1533633003

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go