backups: add remotePath

the main motivation is that id can be used in REST API routes. previously,
the id was a path and this had a "/" in it. This made /api/v1/backups/:backupId
not work.

src/storage/filesystem.js

@@ -1,7 +1,7 @@
 'use strict';
 
 exports = module.exports = {
-    getBasePath,
+    getRootPath,
     checkPreconditions,
 
     upload,
@@ -46,7 +46,7 @@ const assert = require('assert'),
     shell = require('../shell.js');
 
 // storage api
-function getBasePath(apiConfig) {
+function getRootPath(apiConfig) {
     assert.strictEqual(typeof apiConfig, 'object');
 
     switch (apiConfig.provider) {
@@ -78,7 +78,7 @@ async function checkPreconditions(apiConfig, dataLayout, callback) {
 
     debug(`checkPreconditions: ${used} bytes`);
 
-    const [error, result] = await safe(df.file(getBasePath(apiConfig)));
+    const [error, result] = await safe(df.file(getRootPath(apiConfig)));
     if (error) return callback(new BoxError(BoxError.FS_ERROR, `Error when checking for disk space: ${error.message}`));
 
     // Check filesystem is mounted so we don't write into the actual folder on disk
@@ -318,7 +318,7 @@ function testConfig(apiConfig, callback) {
         if (!safe.child_process.execSync(`mountpoint -q -- ${apiConfig.mountPoint}`)) return callback(new BoxError(BoxError.BAD_FIELD, `${apiConfig.mountPoint} is not mounted`));
     }
 
-    const basePath = getBasePath(apiConfig);
+    const basePath = getRootPath(apiConfig);
     const field = apiConfig.provider === PROVIDER_FILESYSTEM ? 'backupFolder' : 'mountPoint';
 
     if (!safe.fs.mkdirSync(path.join(basePath, 'snapshot'), { recursive: true }) && safe.error.code !== 'EEXIST') {