Update DeckhandOperator to do filtering/sorting server-side

This PS updates DeckhandOperator to allow Deckhand to do
filtering/sorting by way of query parameters passed in from
Shipyard, rather than relying on Shipyard to fix up the
response from Deckhand to find the revision with the committed
tag.

This is possible now that Deckhand supports sorting and ordering
as query parameters: https://review.gerrithub.io/#/c/389437/

Change-Id: Idf812faacc78af4acbbbaf9ea5168e64f7333a80

shipyard_airflow/plugins/deckhand_operator.py

@@ -119,8 +119,10 @@ class DeckhandOperator(BaseOperator):
         logging.info("Retrieving revisions information...")
 
         try:
+            query_params = {'tag': 'committed', 'sort': 'id', 'order': 'desc'}
             revisions = yaml.safe_load(requests.get(
-                revision_endpoint, headers=x_auth_token).text)
+                revision_endpoint, headers=x_auth_token,
+                params=query_params).text)
         except requests.exceptions.RequestException as e:
             raise AirflowException(e)
 
@@ -133,14 +135,10 @@ class DeckhandOperator(BaseOperator):
         # Initialize Committed Version
         committed_ver = None
 
-        # Construct revision_list
-        revision_list = revisions.get('results', [])
-
         # Search for the last committed version and save it as xcom
-        for revision in reversed(revision_list):
-            if 'committed' in revision.get('tags'):
-                committed_ver = revision.get('id')
-                break
+        revision_list = revisions.get('results', [])
+        if revision_list:
+            committed_ver = revision_list[-1].get('id')
 
         if committed_ver:
             logging.info("Last committed revision is %d", committed_ver)