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/topology/topo_test.go

@@ -0,0 +1,17 @@
+package topology
+
+import (
+	"testing"
+)
+
+func TestRemoveDataCenter(t *testing.T) {
+	topo := setup(topologyLayout)
+	topo.UnlinkChildNode(NodeId("dc2"))
+	if topo.GetActiveVolumeCount() != 15 {
+		t.Fail()
+	}
+	topo.UnlinkChildNode(NodeId("dc3"))
+	if topo.GetActiveVolumeCount() != 12 {
+		t.Fail()
+	}
+}