Do not fail deploy for empty ceph ansible fetch directory

The RestoreTempDirFromSwift action returned an error if
the Swift container is empty which can stop a deployment.
However there are legitimate reasons the Swift container
could be empty for which the deployment should not be
stopped.

Change-Id: Ic2d9f31caaacbf1c83c4c716cd5e282c6a1953f0
Closes-Bug: #1803609
(cherry picked from commit e05349d55a)

tripleo_common/actions/files.py

@@ -147,6 +147,7 @@ class RestoreTempDirFromSwift(base.TripleOAction):
     ^/tmp/file-mistral-action[A-Za-z0-9_]{6}$
 
     Container should contain a single tarball object
+    If container is empty, then no error is returned
     """
 
     def __init__(self, path, container):
@@ -165,7 +166,9 @@ class RestoreTempDirFromSwift(base.TripleOAction):
         try:
             swiftutils.download_container(swift, self.container, self.path)
             filenames = os.listdir(self.path)
-            if len(filenames) == 1:
+            if len(filenames) == 0:
+                pass
+            elif len(filenames) == 1:
                 tarball.extract_tarball(self.path, filenames[0], remove=True)
             else:
                 msg = "%d objects found in container: %s" \