Merge pull request #9 from baptiste-s/patch-2

[issue-8] add support for ssm parameter with value starting with ami-

functions/lambda.py

@@ -59,11 +59,16 @@ class InstanceRefreshInProgress(LambdaError):
 
 def get_current_image_id():
     """Returns current AMI from SSM"""
+    param_value = None
     param = ssm.get_parameter(Name=SSM_PARAMETER_NAME)
-    param_value = json.loads(param['Parameter']['Value'])
-    image_id = param_value['image_id']
+    value = param['Parameter']['Value']
+    if value.startswith('ami-'):
+        image_id = value
+    else:
+        param_value = json.loads(value)
+        image_id = param_value['image_id']
     logger.info('Newest image_id is "%s"', image_id)
-    return param_value['image_id']
+    return image_id
 
 
 def get_launch_template_name_and_auto_scaling_group():