Add parent directories search for default compose-files

Does not change directory to the parent with the compose-file found.
Works like passing '--file' or setting 'COMPOSE_FILE' with absolute path.
Resolves issue #946.

Signed-off-by: Aleksandr Vinokurov <aleksandr.vin@gmail.com>

compose/cli/utils.py

@@ -62,6 +62,25 @@ def mkdir(path, permissions=0o700):
     return path
 
 
+def find_candidates_in_parent_dirs(filenames, path):
+    """
+    Given a directory path to start, looks for filenames in the
+    directory, and then each parent directory successively,
+    until found.
+
+    Returns tuple (candidates, path).
+    """
+    candidates = [filename for filename in filenames
+                  if os.path.exists(os.path.join(path, filename))]
+
+    if len(candidates) == 0:
+        parent_dir = os.path.join(path, '..')
+        if os.path.abspath(parent_dir) != os.path.abspath(path):
+            return find_candidates_in_parent_dirs(filenames, parent_dir)
+
+    return (candidates, path)
+
+
 def split_buffer(reader, separator):
     """
     Given a generator which yields strings and a separator string,