Switch to concurrent.futures for container prepare/upload

Using process based concurrency doesn't work with mistral's threading
model. Switching to concurrent.futures allows the threading executor
to be used instead.

Change-Id: I2c7a1a7cb8d8e195e041b5b185c1ceba3a6d0e86

requirements.txt

@@ -27,3 +27,4 @@ python-zaqarclient>=1.0.0 # Apache-2.0
 python-keystoneclient>=3.8.0 # Apache-2.0
 keystoneauth1>=3.4.0 # Apache-2.0
 tenacity>=4.4.0 # Apache-2.0
+futures>=3.0.0;python_version=='2.7' or python_version=='2.6'  # BSD

setup.cfg

@@ -81,6 +81,7 @@ mistral.actions =
     tripleo.config.download_config = tripleo_common.actions.config:DownloadConfigAction
     tripleo.config.get_overcloud_config = tripleo_common.actions.config:GetOvercloudConfig
     tripleo.container_images.prepare = tripleo_common.actions.container_images:PrepareContainerImageEnv
+    tripleo.container_images.prepare_upload = tripleo_common.actions.container_images:PrepareUploadContainerImages
     tripleo.deployment.config = tripleo_common.actions.deployment:OrchestrationDeployAction
     tripleo.deployment.deploy = tripleo_common.actions.deployment:DeployStackAction
     tripleo.deployment.overcloudrc = tripleo_common.actions.deployment:OvercloudRcAction

tripleo_common/image/image_uploader.py

@@ -15,9 +15,9 @@
 
 
 import abc
+from concurrent import futures
 import json
 import logging
-import multiprocessing
 import netifaces
 import os
 import requests
@@ -323,7 +323,7 @@ class DockerImageUploader(ImageUploader):
         for image in images:
             discover_args.append((image, tag_from_label,
                                   self.insecure_registries))
-        p = multiprocessing.Pool(16)
+        p = futures.ThreadPoolExecutor(max_workers=16)
 
         versioned_images = {}
         for image, versioned_image in p.map(discover_tag_from_inspect,
@@ -376,7 +376,7 @@ class DockerImageUploader(ImageUploader):
 
         # workers will be half the CPU count, to a minimum of 2
         workers = max(2, processutils.get_worker_count() // 2)
-        p = multiprocessing.Pool(workers)
+        p = futures.ThreadPoolExecutor(max_workers=workers)
 
         for result in p.map(docker_upload, self.upload_tasks):
             local_images.extend(result)

tripleo_common/tests/image/test_image_uploader.py

@@ -396,7 +396,7 @@ class TestDockerImageUploader(base.TestCase):
             ('docker.io/t/foo', 'rdo_version', sr)
         )
 
-    @mock.patch('multiprocessing.Pool')
+    @mock.patch('concurrent.futures.ThreadPoolExecutor')
     def test_discover_image_tags(self, mock_pool):
         mock_pool.return_value.map.return_value = (
             ('docker.io/t/foo', 'a'),