Added support for creation date to Ami

moto/ec2/models.py

@@ -911,6 +911,7 @@ class Ami(TaggedEC2Resource):
         self.architecture = None
         self.kernel_id = None
         self.platform = None
+        self.creation_date = datetime.utcnow().isoformat()
 
         if instance:
             self.instance = instance

moto/ec2/responses/amis.py

@@ -90,6 +90,7 @@ DESCRIBE_IMAGES_RESPONSE = """<DescribeImagesResponse xmlns="http://ec2.amazonaw
           <kernelId>{{ image.kernel_id }}</kernelId>
           <ramdiskId>ari-1a2b3c4d</ramdiskId>
           <imageOwnerAlias>amazon</imageOwnerAlias>
+          <creationDate>{{ image.creation_date }}</creationDate>
           <name>{{ image.name }}</name>
           {% if image.platform %}
              <platform>{{ image.platform }}</platform>