Fix exception when updating container with metadata

A ValueError is raised when running the object_container module with the
`metadata` param against a container with existing metadata.

When the module attempts to enumerate the existing container metadata, a
ValueError exception is raised, because the code is iterating over the
metadata keys, instead of `dict_items`.
Compare to the iteration through another dict `metadata` on the next
line:

    new_metadata = dict((k, v) for k, v in metadata.items()

This change adds a call to `items()` on the dictionary.
Note that this is added outside the parentheses so that the behaviour of the
`or` statement is not affected, and that another exception isn't caused
if `container.metadata` is not a dict.

Closes-Bug: #2071934
Change-Id: Ie5e1f275839e38340a75ab18c3b9ec9bc7745d68

ci/roles/object_container/tasks/main.yml

@@ -31,6 +31,21 @@
       - ('cache-control' in container.container.metadata.keys()|map('lower'))
       - container.container.metadata['foo'] == 'bar'
 
+- name: Update container metadata
+  openstack.cloud.object_container:
+    cloud: "{{ cloud }}"
+    name: ansible_container
+    metadata:
+      'foo': 'baz'
+  register: container
+
+- name: Verify container metadata was updated
+  assert:
+    that:
+      - container is changed
+      - ('cache-control' in container.container.metadata.keys()|map('lower'))
+      - container.container.metadata['foo'] == 'baz'
+
 - name: Update a container
   openstack.cloud.object_container:
     cloud: "{{ cloud }}"
@@ -45,7 +60,7 @@
     that:
       - container is changed
       - ('cache-control' not in container.container.metadata.keys()|map('lower'))
-      - "container.container.metadata == {'foo': 'bar'}"
+      - "container.container.metadata == {'foo': 'baz'}"
       - container.container.read_ACL is none or container.container.read_ACL == ""
 
 - name: Delete container

plugins/modules/object_container.py

@@ -269,7 +269,7 @@ class ContainerModule(OpenStackModule):
         if metadata is not None:
             # Swift metadata keys must be treated as case-insensitive
             old_metadata = dict((k.lower(), v)
-                                for k, v in (container.metadata or {}))
+                                for k, v in (container.metadata or {}).items())
             new_metadata = dict((k, v) for k, v in metadata.items()
                                 if k.lower() not in old_metadata
                                 or v != old_metadata[k.lower()])