[config][generic-update] Implementing patch sorting (#1599)

#### What I did
Implemented [JSON Patch Ordering using YANG Models Design Doc](https://github.com/Azure/SONiC/blob/master/doc/config-generic-update-rollback/Json_Patch_Ordering_using_YANG_Models_Design.md)

#### How I did it

#### How to verify it
Unit-Tests

#### Previous command output (if the output of a command-line utility has changed)

#### New command output (if the output of a command-line utility has changed)

generic_config_updater/generic_updater.py

@@ -3,6 +3,7 @@
 from enum import Enum
 from .gu_common import GenericConfigUpdaterError, ConfigWrapper, \
                        DryRunConfigWrapper, PatchWrapper
+from .patch_sorter import PatchSorter
 
 CHECKPOINTS_DIR = "/etc/sonic/checkpoints"
 CHECKPOINT_EXT = ".cp.json"
@@ -16,11 +17,6 @@ def release_lock(self):
         # TODO: Implement ConfigLock
         pass
 
-class PatchSorter:
-    def sort(self, patch):
-        # TODO: Implement patch sorter
-        raise NotImplementedError("PatchSorter.sort(patch) is not implemented yet")
-
 class ChangeApplier:
     def apply(self, change):
         # TODO: Implement change applier
@@ -36,7 +32,7 @@ def __init__(self,
                  changeapplier=None,
                  config_wrapper=None,
                  patch_wrapper=None):
-        self.patchsorter = patchsorter if patchsorter is not None else PatchSorter()
+        self.patchsorter = patchsorter if patchsorter is not None else PatchSorter(config_wrapper, patch_wrapper)
         self.changeapplier = changeapplier if changeapplier is not None else ChangeApplier()
         self.config_wrapper = config_wrapper if config_wrapper is not None else ConfigWrapper()
         self.patch_wrapper = patch_wrapper if patch_wrapper is not None else PatchWrapper()