Merge pull request #219 from joekiller/ami_filter_state

allow get_filter_value to return state of ami and test

moto/ec2/models.py

@@ -604,6 +604,12 @@ class Ami(TaggedEC2Instance):
             return getattr(self,filter_name)
         elif filter_name == 'image-id':
             return self.id
+        elif filter_name == 'state':
+            return self.state
+        elif filter_name.startswith('tag:'):
+            tag_name = filter_name.replace('tag:', '', 1)
+            tags = dict((tag['key'], tag['value']) for tag in self.get_tags())
+            return tags.get(tag_name)
         else:
             ec2_backend.raise_not_implemented_error("The filter '{0}' for DescribeImages".format(filter_name))