Add docker_images script that absorbs some of the redundancy in…

Add docker_images script that absorbs some of the redundancy in balancecontainers and check_dockerfile_coverage.py

util/docker_images.py

+import yaml
+import os
+import pathlib2
+import itertools
+import sys
+
+TRAVIS_BUILD_DIR = os.environ.get("TRAVIS_BUILD_DIR")
+CONFIG_FILE_PATH = pathlib2.Path(TRAVIS_BUILD_DIR, "util", "parsefiles_config.yml")
+
+def get_used_images(images):
+    """
+    Returns the images and their ranks that are scheduled to be built and that exist in the configuration file.
+
+    Input:
+    images: A set of Docker images
+    """
+
+    # open config file containing container weights
+    config_file_path = pathlib2.Path(CONFIG_FILE_PATH)
+
+    with (config_file_path.open(mode='r')) as file:
+        try:
+            config = yaml.load(file)
+        except yaml.YAMLError, exc:
+            LOGGER.error("error in configuration file: %s" % str(exc))
+            sys.exit(1)
+
+    # get container weights
+    weights = config.get("weights")
+
+    # convert all images in config file to a list of tuples (<image>, <weight>)
+    weights_list = [x.items() for x in weights]
+    weights_list = list(itertools.chain.from_iterable(weights_list))
+
+    # performs intersection between weighted images and input images
+    return [x for x in weights_list if x[0] in images]