Bug 1302596: Retry image download when it fails

We already have retries for when the download fails, but not when the
downloaded image is corrupted.

We add a retry for the general `ensureImage()` function, for edge cases
like above.

As we are not retrying because of possible network temporary outage, we
configure the waiting time to be a small value.

src/lib/docker/artifact_image.js

@@ -224,6 +224,7 @@ class ArtifactImage {
 
       return true;
     } catch(e) {
+      this.stream.write(fmtLog(`Downloaded image is corrupted: ${e.message}`));
       delete this.knownHashes[`${this.taskId}-${this.artifactPath}`];
       return false;
     }

src/lib/task.js

@@ -25,6 +25,7 @@ const uploadToS3 = require('./upload_to_s3');
 const _ = require('lodash');
 const EventEmitter = require('events');
 const libUrls = require('taskcluster-lib-urls');
+const promiseTry = require('promise-retry');
 
 let debug = new Debug('runTask');
 
@@ -869,10 +870,21 @@ class Task extends EventEmitter {
     let imageId;
     try {
       let im = this.runtime.imageManager;
-      imageId = await im.ensureImage(this.task.payload.image,
-        this.stream,
-        this,
-        this.task.scopes);
+
+      imageId = await promiseRetry(retry => {
+        return im.ensureImage(
+          this.task.payload.image,
+          this.stream,
+          this,
+          this.task.scopes).catch(retry);
+      }, {
+        maxTimeout: 1000,
+        minTimeout: 10,
+        factor: 1.2,
+        randomize: true,
+        retries: 3,
+      });
+
       this.imageHash = imageId;
       this.runtime.gc.markImage(imageId);
     } catch (e) {