storage: Directory shouldn't be listed as type 'file'

Fix internals of libvirt for new storage volume type.
Libvirt reported an invalid type of the volume.

BZ #727088

include/libvirt/libvirt.h.in

@@ -1705,6 +1705,7 @@ typedef virStorageVol *virStorageVolPtr;
 typedef enum {
   VIR_STORAGE_VOL_FILE = 0,     /* Regular file based volumes */
   VIR_STORAGE_VOL_BLOCK = 1,    /* Block based volumes */
+  VIR_STORAGE_VOL_DIR = 2,      /* Directory-passthrough based volume */
 } virStorageVolType;
 
 typedef enum {

src/storage/storage_backend_fs.c

@@ -675,6 +675,10 @@ virStorageBackendFileSystemRefresh(virConnectPtr conn ATTRIBUTE_UNUSED,
                 goto cleanup;
         }
 
+        /* directory based volume */
+        if (vol->target.format == VIR_STORAGE_FILE_DIR)
+            vol->type = VIR_STORAGE_VOL_DIR;
+
         if (backingStore != NULL) {
             vol->backingStore.path = backingStore;
             vol->backingStore.format = backingStoreFormat;