inventory: Add !vault yaml tag

Otherwise the inventory script will stacktrace while parsing !vault tags

inventory

@@ -8,6 +8,30 @@ import json
 import argparse
 import collections as coll
 
+
+# https://stackoverflow.com/questions/43058050/creating-custom-tag-in-pyyaml
+
+class VaultTag(yaml.YAMLObject):
+    yaml_tag = u'!vault'
+
+    def __init__(self, env_var):
+        self.env_var = env_var
+
+    def __repr__(self):
+        v = os.environ.get(self.env_var) or ''
+        return 'VaultTag({}, contains={})'.format(self.env_var, v)
+
+    @classmethod
+    def from_yaml(cls, loader, node):
+        return VaultTag(node.value)
+
+    @classmethod
+    def to_yaml(cls, dumper, data):
+        return dumper.represent_scalar(cls.yaml_tag, data.env_var)
+
+# Required for safe_load
+yaml.SafeLoader.add_constructor('!vault', VaultTag.from_yaml)
+
 inventory_defaults = {
     'ansible_ssh_port': 22022,
     'ansible_ssh_user': 'root'