plugin: enable import for nfs/btrfs/cifs/cephfs/glusterfs

and reuse the DirPlugin implementation

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
Reviewed-by: Fiona Ebner <f.ebner@proxmox.com>

src/PVE/Storage/BTRFSPlugin.pm

@@ -40,6 +40,7 @@ sub plugindata {
 		backup => 1,
 		snippets => 1,
 		none => 1,
+		import => 1,
 	    },
 	    { images => 1, rootdir => 1 },
 	],
@@ -963,4 +964,8 @@ sub rename_volume {
     return "${storeid}:$target_volname";
 }
 
+sub get_import_metadata {
+    return PVE::Storage::DirPlugin::get_import_metadata(@_);
+}
+
 1