Fix exit(2) on SIGHUP before fully initialized.

Fixes #244

Author: JoelLinn

cmd/docker-gen/main.go

@@ -5,7 +5,9 @@ import (
 	"fmt"
 	"log"
 	"os"
+	"os/signal"
 	"path/filepath"
+	"syscall"
 
 	"github.com/BurntSushi/toml"
 	docker "github.com/fsouza/go-dockerclient"
@@ -113,6 +115,10 @@ func initFlags() {
 }
 
 func main() {
+	// SIGHUP is used to trigger generation but go programs call os.Exit(2) at default.
+	// Ignore the signal until the handler is registered:
+	signal.Ignore(syscall.SIGHUP)
+
 	initFlags()
 
 	if version {