Use an EscoDB task to batch-save docs during migration

Author: jcoglan

lib/legacy/migrator.js

@@ -57,15 +57,20 @@ class Migrator {
   }
 
   async _copySettings () {
-    let copies = [['/global', this._data.global]];
+    let writer = this._store.task()
+    let reader = this._store.task()
+
+    let docs = [['/global', this._data.global]];
 
     for (let service in this._data.services) {
-      copies.push(['/services/' + service, this._data.services[service]])
+      docs.push(['/services/' + service, this._data.services[service]])
     }
 
-    for (let [key, value] of copies) {
-      await this._store.update(key, () => value)
-      let stored = await this._store.get(key)
+    let writes = docs.map(([key, value]) => writer.update(key, () => value))
+    await Promise.all(writes)
+
+    for (let [key, value] of docs) {
+      let stored = await reader.get(key)
 
       assert.deepEqual(value, stored,
         'failed to write: [' + key + '] ' + JSON.stringify(value))