[IMP] runbot_merge: add logging to PR sync and reset error PRs to open

The choice to keep sync'd PRs in error means it's possible to update
the code and re-run the PR directly without it going through review &
CI again, which is a bit odd. Remove the special case and always reset
a sync'd PR to opened for clarity and simplicity.

closes #71
closes #83

runbot_merge/controllers/__init__.py

@@ -157,11 +157,19 @@ def handle_pr(env, event):
                 pr_obj.repository.name, pr_obj.number,
                 event['sender']['login']
             )
-        if pr_obj.state != 'error':
-            pr_obj.state = 'opened'
 
-        pr_obj.head = pr['head']['sha']
-        pr_obj.squash = pr['commits'] == 1
+        _logger.info(
+            "PR %s:%s updated to %s by %s, resetting to 'open' and squash=%s",
+            pr_obj.repository.name, pr_obj.number,
+            pr['head']['sha'], event['sender']['login'],
+            pr['commits'] == 1
+        )
+
+        pr_obj.write({
+            'state': 'opened',
+            'head': pr['head']['sha'],
+            'squash': pr['commits'] == 1,
+        })
         return 'Updated {} to {}'.format(pr_obj.id, pr_obj.head)
 
     # don't marked merged PRs as closed (!!!)

runbot_merge/tests/test_basic.py

@@ -1563,7 +1563,7 @@ class TestPRUpdate(object):
         c2 = repo.make_commit(c, 'first', None, tree={'m': 'cc'})
         prx.push(c2)
         assert pr.head == c2
-        assert pr.state == 'error'
+        assert pr.state == 'opened'
 
     def test_unknown_pr(self, env, repo):
         m = repo.make_commit(None, 'initial', None, tree={'m': 'm'})