tasks: rework the startTask API

it is now async. change was required to reset the pending flag

src/dns.js

@@ -377,6 +377,6 @@ async function startSyncDnsRecords(options) {
     assert.strictEqual(typeof options, 'object');
 
     const taskId = await tasks.add(tasks.TASK_SYNC_DNS_RECORDS, [ options ]);
-    tasks.startTask(taskId, {});
+    safe(tasks.startTask(taskId, {}), { debug }); // background
     return taskId;
 }