Set service volume size with kompose.volume.size label (#235)

1. Copy labels from compose to kobject
2. If kompose.volume.size is set on service level, use it

Internal API changes:

- Add PVCSize to kobject Volumes struct
- Pass default volume size as CreatePVC() param

pkg/kobject/kobject.go

@@ -142,4 +142,5 @@ type Volumes struct {
 	Container  string // Mountpath
 	Mode       string // access mode for volume
 	PVCName    string // name of PVC
+	PVCSize    string // PVC size
 }