Additional method on the SaltYamlSafeLoader class in yamlloader.py to fix YAML merging

yamlloader.py

class SaltYamlSafeLoader(yaml.SafeLoader, object):
	def flatten_mapping(self, node):
		merge = []
		index = 0
		while index < len(node.value):
			key_node, value_node = node.value[index]

			if key_node.tag == u'tag:yaml.org,2002:merge':
				del node.value[index]
				if isinstance(value_node, MappingNode):
					self.flatten_mapping(value_node)
					merge.extend(value_node.value)
				elif isinstance(value_node, SequenceNode):
					submerge = []
					for subnode in value_node.value:
						if not isinstance(subnode, MappingNode):
							raise ConstructorError("while constructing a mapping",
									node.start_mark,
									"expected a mapping for merging, but found %s"
									% subnode.id, subnode.start_mark)
						self.flatten_mapping(subnode)
						submerge.append(subnode.value)
					submerge.reverse()
					for value in submerge:
						merge.extend(value)
				else:
					raise ConstructorError("while constructing a mapping", node.start_mark,
							"expected a mapping or list of mappings for merging, but found %s"
							% value_node.id, value_node.start_mark)
			elif key_node.tag == u'tag:yaml.org,2002:value':
				key_node.tag = u'tag:yaml.org,2002:str'
				index += 1
			else:
				index += 1
		if merge:
			# Here we need to discard any duplicate entries based on key_node
			existing_nodes = [name_node.value for name_node, value_node in node.value]
			mergeable_items = [x for x in merge if x[0].value not in existing_nodes]

			node.value = mergeable_items + node.value