system: add tests for fs usage route

src/system.js

@@ -240,10 +240,10 @@ class FilesystemUsageTask extends AsyncTask {
             this.emitData({ speed: -1 });
         }
 
-        const dockerDf = await docker.df();
+        const dockerDf = await docker.df({ abortSignal: signal });
 
         for (const content of contents) {
-            percent += (100/contents.length);
+            percent += (90/contents.length+1);
             if (signal.aborted) return;
 
             this.emitProgress(percent,`Checking du of ${content.id} ${content.path}`);