eventlog: add backup target eventlog

src/test/system-test.js

@@ -94,7 +94,7 @@ describe('System', function () {
         const usageTask = await system.getFilesystemUsage(rootFs.filesystem);
 
         return new Promise((resolve, reject) => {
-            usageTask.on('data', (type, data) => console.log(type, data));
+            // usageTask.on('data', (type, data) => console.log(type, data));
             usageTask.on('done', (error) => {
                 if (error.errorMessage) reject(new Error(error.errorMessage)); else resolve();
             });