Refactor GCE wrapper library to allow execution from E2E test suite

This reverts commit 147b6911f5, reversing
changes made to 6fd986065b.

pkg/volume/testing.go

@@ -92,6 +92,11 @@ func (f *fakeVolumeHost) NewWrapperCleaner(spec *Spec, podUID types.UID) (Cleane
 	return plug.NewCleaner(spec.Name(), podUID)
 }
 
+// Returns the hostname of the host kubelet is running on
+func (f *fakeVolumeHost) GetHostName() string {
+	return "fakeHostName"
+}
+
 func ProbeVolumePlugins(config VolumeConfig) []VolumePlugin {
 	if _, ok := config.OtherAttributes["fake-property"]; ok {
 		return []VolumePlugin{