chore(xo-server): move LVM start hook to file restore NG

Otherwise, I have a feeling that we may forget to migrate this code when
legacy backup code will be retired.

packages/xo-server/src/xo-mixins/backups.js

@@ -300,14 +300,6 @@ const mountLvmPv = (device, partition) => {
 export default class {
   constructor (xo) {
     this._xo = xo
-
-    // clean any LVM volumes that might have not been properly
-    // unmounted
-    xo.on('start', () =>
-      Promise.all([execa('losetup', ['-D']), execa('vgchange', ['-an'])]).then(
-        () => execa('pvscan', ['--cache'])
-      )
-    )
   }
 
   async listRemoteBackups (remoteId) {

packages/xo-server/src/xo-mixins/file-restore-ng.js

@@ -163,6 +163,13 @@ export default class BackupNgFileRestore {
   constructor (app) {
     this._app = app
     this._mounts = { __proto__: null }
+
+    // clean any LVM volumes that might have not been properly
+    // unmounted
+    app.on('start', async () => {
+      await Promise.all([execa('losetup', ['-D']), execa('vgchange', ['-an'])])
+      await execa('pvscan', ['--cache'])
+    })
   }
 
   @defer