Prevent the migration of VM with 'optimize' False in VM metadata

This patch adds the functionality to filter out VMs which have
metadata field 'optimize' set to False. This patch implements the
functionality for basic_consolidation strategy.

Change-Id: Iaf7b63e09534e4a67406e7f092242558b78c0bde
Partially-Implements: BP audit-tag-vm-metadata

watcher/objects/fields.py

@@ -17,6 +17,7 @@
 import ast
 import six
 
+from oslo_serialization import jsonutils
 from oslo_versionedobjects import fields
 
 
@@ -96,8 +97,26 @@ class FlexibleListOfDictField(fields.AutoTypedField):
         super(FlexibleListOfDictField, self)._null(obj, attr)
 
 
+class Json(fields.FieldType):
+    def coerce(self, obj, attr, value):
+        if isinstance(value, six.string_types):
+            loaded = jsonutils.loads(value)
+            return loaded
+        return value
+
+    def from_primitive(self, obj, attr, value):
+        return self.coerce(obj, attr, value)
+
+    def to_primitive(self, obj, attr, value):
+        return jsonutils.dumps(value)
+
+
+class JsonField(fields.AutoTypedField):
+    AUTO_TYPE = Json()
+
 # ### Notification fields ### #
 
+
 class BaseWatcherEnum(Enum):
 
     ALL = ()