AWS: handle 'InvalidConversionTaskId.Malformed' error

When we call the describe_import_image_tasks paginator with a
task id specified and that task id does not exist, AWS can return
a InvalidConversionTaskId.Malformed error instead of the expected
empty list.  Handle that case and add a test for it.

Change-Id: I1a3a9297e123a50a4beeb7e18124b8cc17aa28bb

nodepool/driver/aws/adapter.py

@@ -824,10 +824,19 @@ class AwsAdapter(statemachine.Adapter):
         paginator = self.ec2_client.get_paginator(
             'describe_import_image_tasks')
         with self.non_mutating_rate_limiter:
-            for page in paginator.paginate(ImportTaskIds=[task_id]):
-                for task in page['ImportImageTasks']:
-                    # Return the first and only task
-                    return task
+            try:
+                for page in paginator.paginate(ImportTaskIds=[task_id]):
+                    for task in page['ImportImageTasks']:
+                        # Return the first and only task
+                        return task
+            except botocore.exceptions.ClientError as error:
+                if (error.response['Error']['Code'] ==
+                    'InvalidConversionTaskId.Malformed'):
+                    # In practice, this can mean that the task no
+                    # longer exists
+                    pass
+                else:
+                    raise
         return None
 
     def _listImportSnapshotTasks(self):

nodepool/tests/unit/fake_aws.py

@@ -120,6 +120,10 @@ class ImportImageTaskPaginator:
         if 'ImportTaskIds' in kw:
             tasks = [t for t in tasks
                      if t['ImportTaskId'] in kw['ImportTaskIds']]
+            if not tasks:
+                raise botocore.exceptions.ClientError(
+                    {'Error': {'Code': 'InvalidConversionTaskId.Malformed'}},
+                    'DescribeImportImageTasks')
         # A page of tasks
         ret = [{'ImportImageTasks': tasks}]
 

nodepool/tests/unit/test_driver_aws.py

@@ -1042,6 +1042,14 @@ class TestDriverAws(tests.DBTestCase):
                 # Probably not found
                 break
 
+    def test_aws_get_import_image_task(self):
+        # A unit test of the unusual error handling for missing tasks
+        configfile = self.setup_config('aws/diskimage.yaml')
+        pool = self.useNodepool(configfile, watermark_sleep=1)
+        self.startPool(pool)
+        adapter = pool.getProviderManager('ec2-us-west-2').adapter
+        self.assertIsNone(adapter._getImportImageTask("fake-id"))
+
     def test_aws_provisioning_spot_instances(self):
         # Test creating a spot instances instead of an on-demand on.
         req = self.requestNode('aws/aws-spot.yaml', 'ubuntu1404-spot')