Add option to not log shell subprocess stdout+stderr

When tailing the box log file this leads to logline recursion

src/logs.js

@@ -60,7 +60,7 @@ function tail(filePaths, options) {
     const args = [ LOGTAIL_CMD, '--lines=' + lines ];
     if (options.follow) args.push('--follow');
 
-    return shell.sudo('tail', args.concat(filePaths), { streamStdout: true }, () => {});
+    return shell.sudo('tail', args.concat(filePaths), { streamStdout: true, dropStdout: true, dropStdErr: true }, () => {});
 }
 
 function journalctl(unit, options) {

src/shell.js

@@ -111,10 +111,10 @@ function sudo(tag, args, options, callback) {
 
     cp.stdout.on('data', (data) => {
         if (options.captureStdout) stdoutResult += data.toString('utf8');
-        process.stdout.write(data); // do not use debug to avoid double timestamps when calling backupupload.js
+        if (!options.dropStdout) process.stdout.write(data); // do not use debug to avoid double timestamps when calling backupupload.js
     });
     cp.stderr.on('data', (data) => {
-        process.stderr.write(data);  // do not use debug to avoid double timestamps when calling backupupload.js
+        if (!options.dropStderr) process.stderr.write(data);  // do not use debug to avoid double timestamps when calling backupupload.js
     });
 
     cp.on('exit', function (code, signal) {