directory structure change to work with glide

glide has its own requirements. My previous workaround caused me some
code checkin errors. Need to fix this.

weed/operation/list_masters.go

@@ -0,0 +1,32 @@
+package operation
+
+import (
+	"encoding/json"
+
+	"github.com/chrislusf/seaweedfs/weed/glog"
+	"github.com/chrislusf/seaweedfs/weed/util"
+)
+
+type ClusterStatusResult struct {
+	IsLeader bool     `json:"IsLeader,omitempty"`
+	Leader   string   `json:"Leader,omitempty"`
+	Peers    []string `json:"Peers,omitempty"`
+}
+
+func ListMasters(server string) ([]string, error) {
+	jsonBlob, err := util.Get("http://" + server + "/cluster/status")
+	glog.V(2).Info("list masters result :", string(jsonBlob))
+	if err != nil {
+		return nil, err
+	}
+	var ret ClusterStatusResult
+	err = json.Unmarshal(jsonBlob, &ret)
+	if err != nil {
+		return nil, err
+	}
+	masters := ret.Peers
+	if ret.IsLeader {
+		masters = append(masters, ret.Leader)
+	}
+	return masters, nil
+}