rework backup root

notes:
* backup root cannot come from backend. for dynamic mounts backend cannot know where it is mounted
* backupConfig is 3 parts - format / mount / password . there is also this rootPath (which should not be in db)
* password should be stored separately in settings at some point
* format has to be passed along everywhere because we allow restore from  same backupConfig but different format. we do this by saving the format in the backups table

fixes #819

src/apptask.js

@@ -15,6 +15,7 @@ const apps = require('./apps.js'),
     appstore = require('./appstore.js'),
     assert = require('assert'),
     AuditSource = require('./auditsource.js'),
+    backups = require('./backups.js'),
     backuptask = require('./backuptask.js'),
     BoxError = require('./boxerror.js'),
     constants = require('./constants.js'),
@@ -319,17 +320,9 @@ async function install(app, args, progressCallback) {
         await services.setupAddons(app, app.manifest.addons);
         await services.clearAddons(app, app.manifest.addons);
         const backupConfig = restoreConfig.backupConfig;
-        let mountObject = null;
-        if (mounts.isManagedProvider(backupConfig.provider)) {
-            await progressCallback({ percent: 70, message: 'Setting up mount for importing' });
-            mountObject = {  // keep this in sync with importApp in apps.js
-                name:  `appimport-${app.id}`,
-                hostPath: `/mnt/appimport-${app.id}`,
-                mountType: backupConfig.provider,
-                mountOptions: backupConfig.mountOptions
-            };
-            await mounts.tryAddMount(mountObject, { timeout: 10 });
-        }
+        const mountObject = await backups.setupStorage(backupConfig, `/mnt/appimport-${app.id}`);
+        if (mountObject) await progressCallback({ percent: 70, message: 'Setting up mount for importing' });
+        backupConfig.rootPath = backups.getRootPath(backupConfig, `/mnt/appimport-${app.id}`);
         await backuptask.downloadApp(app, restoreConfig, (progress) => { progressCallback({ percent: 75, message: progress.message }); });
         await apps.restoreConfig(app);
         if (mountObject) await mounts.removeMount(mountObject);