windows: support -dev mode

Support running `nomad agent -dev` in Windows, by setting proper network
interface.

Prior to this change, `nomad` uses `lo` interface but Windows uses
"Loopback Pseudo-Interface 1" to refer to loopback device interface:
https://github.com/golang/go/blob/go1.14.1/src/net/net_windows_test.go#L304-L318
.

command/agent/config.go

@@ -743,6 +743,11 @@ func newDevModeConfig(devMode, connectMode bool) (*devModeConfig, error) {
 }
 
 func (mode *devModeConfig) networkConfig() error {
+	if runtime.GOOS == "windows" {
+		mode.bindAddr = "127.0.0.1"
+		mode.iface = "Loopback Pseudo-Interface 1"
+		return nil
+	}
 	if runtime.GOOS == "darwin" {
 		mode.bindAddr = "127.0.0.1"
 		mode.iface = "lo0"