support command line arguments in a configuration file so we can weed master -config=master.conf, weed volume -config=volume.conf and etc.

weed/command/command.go

@@ -1,8 +1,8 @@
 package command
 
 import (
-	"flag"
 	"fmt"
+	flag "github.com/chrislusf/seaweedfs/weed/util/fla9"
 	"os"
 	"strings"
 )