Add facility to deepcopy bound methods in Py2.6 and apply to grains

In #28587, we failed to account for the inability of Py2.6 to deepcopy bound methods. This provides a workaround for that.

salt/modules/grains.py

@@ -15,6 +15,7 @@ import collections
 from functools import reduce
 
 # Import 3rd-party libs
+import salt.utils.copy
 from salt.utils.odict import OrderedDict
 import yaml
 import salt.ext.six as six
@@ -238,8 +239,15 @@ def setvals(grains, destructive=False):
             grains[key] = val
             __grains__[key] = val
     # Cast defaultdict to dict; is there a more central place to put this?
-    yaml_reps = copy.deepcopy(yaml.representer.SafeRepresenter.yaml_representers)
-    yaml_multi_reps = copy.deepcopy(yaml.representer.SafeRepresenter.yaml_multi_representers)
+    try:
+        yaml_reps = copy.deepcopy(yaml.representer.SafeRepresenter.yaml_representers)
+        yaml_multi_reps = copy.deepcopy(yaml.representer.SafeRepresenter.yaml_multi_representers)
+    except (TypeError, NameError):
+        # This likely means we are running under Python 2.6 which cannot deepcopy
+        # bound methods. Fallback to a modification of deepcopy which can support
+        # this behavoir.
+        yaml_reps = salt.utils.copy.deepcopy_bound(yaml.representer.SafeRepresenter.yaml_representers)
+        yaml_multi_reps = salt.utils.copy.deepcopy_bound(yaml.representer.SafeRepresenter.yaml_multi_representers)
     yaml.representer.SafeRepresenter.add_representer(collections.defaultdict,
             yaml.representer.SafeRepresenter.represent_dict)
     yaml.representer.SafeRepresenter.add_representer(OrderedDict,

salt/utils/copy.py

@@ -0,0 +1,33 @@
+# -*- coding: utf-8 -*-
+'''
+Compatibility functions for copying
+'''
+
+# Import python libs
+from __future__ import absolute_import
+import copy
+import types
+
+
+def deepcopy_bound(name):
+    '''
+    Compatibility helper function to allow copy.deepcopy copy bound methods
+    which is broken on Python 2.6, due to the following bug:
+    https://bugs.python.org/issue1515
+
+    Warnings:
+        - This method will mutate the global deepcopy dispatcher, which means that
+        this function is NOT threadsafe!
+
+        - Not Py3 compatable. The intended use case is deepcopy compat for Py2.6
+
+    '''
+    def _deepcopy_method(x, memo):
+        return type(x)(x.im_func, copy.deepcopy(x.im_self, memo), x.im_class)  # pylint: disable=W1699
+    try:
+        pre_dispatch = copy._deepcopy_dispatch
+        copy._deepcopy_dispatch[types.MethodType] = _deepcopy_method
+        ret = copy.deepcopy(name)
+    finally:
+        copy._deepcopy_dispatch = pre_dispatch
+    return ret