Initialize _keys in __init__() in FakeFlavorResource

_keys is defined as a class attribute in FakeFlavorResource. So when
we call set_keys() to update it, it changes. And this change may bring
trouble to the other tests afterward.

So define and initialize it in __init__() as an object attribute.

Change-Id: Ib18c03877b67e1b7c2e107f598076b928a58e4fb
Closes-bug: #1548378

openstackclient/tests/compute/v2/fakes.py

@@ -372,8 +372,11 @@ class FakeFlavorResource(fakes.FakeResource):
     Need to fake them, otherwise the functions to be tested won't run properly.
     """
 
-    # Fake properties.
-    _keys = {'property': 'value'}
+    def __init__(self, manager=None, info={}, loaded=False, methods={}):
+        super(FakeFlavorResource, self).__init__(manager, info,
+                                                 loaded, methods)
+        # Fake properties.
+        self._keys = {'property': 'value'}
 
     def set_keys(self, args):
         self._keys.update(args)