Simplify FactCache.copy()

Also fix the bug (missing from six import iteritems) I introduced in
823677b4.

lib/ansible/plugins/cache/__init__.py

@@ -60,7 +60,7 @@ class FactCache(MutableMapping):
 
     def copy(self):
         """ Return a primitive copy of the keys and values from the cache. """
-        return dict([(k, v) for (k, v) in iteritems(self)])
+        return dict(self)
 
     def keys(self):
         return self._plugin.keys()

test/units/plugins/cache/test_cache.py

@@ -19,7 +19,8 @@
 from __future__ import (absolute_import, division, print_function)
 __metaclass__ = type
 
-from ansible.compat.tests import unittest
+from ansible.compat.tests import unittest, mock
+from ansible.plugins.cache import FactCache
 from ansible.plugins.cache.base import BaseCacheModule
 from ansible.plugins.cache.memory import CacheModule as MemoryCache
 
@@ -42,6 +43,20 @@ else:
     from ansible.plugins.cache.redis import CacheModule as RedisCache
 
 
+class TestFactCache(unittest.TestCase):
+
+    def setUp(self):
+        with mock.patch('ansible.constants.CACHE_PLUGIN', 'memory'):
+            self.cache = FactCache()
+
+    def test_copy(self):
+        self.cache['avocado'] = 'fruit'
+        self.cache['daisy'] = 'flower'
+        a_copy = self.cache.copy()
+        self.assertEqual(type(a_copy), dict)
+        self.assertEqual(a_copy, dict(avocado='fruit', daisy='flower'))
+
+
 class TestAbstractClass(unittest.TestCase):
 
     def setUp(self):