api: expose merge message in the merge operation

rhodecode/api/tests/test_merge_pull_request.py

@@ -109,6 +109,7 b' class TestMergePullRequest(object):'
         expected = {
             'executed': True,
             'failure_reason': 0,
+            'merge_status_message': 'This pull request can be automatically merged.',
             'possible': True,
             'merge_commit_id': pull_request.shadow_merge_ref.commit_id,
             'merge_ref': pull_request.shadow_merge_ref._asdict()

rhodecode/api/views/pull_request_api.py

@@ -267,10 +267,11 b' def merge_pull_request('
 
         "id": <id_given_in_input>,
         "result": {
-            "executed":         "<bool>",
-            "failure_reason":   "<int>",
-            "merge_commit_id":  "<merge_commit_id>",
-            "possible":         "<bool>",
+            "executed":               "<bool>",
+            "failure_reason":         "<int>",
+            "merge_status_message":   "<str>",
+            "merge_commit_id":        "<merge_commit_id>",
+            "possible":               "<bool>",
             "merge_ref":        {
                                     "commit_id": "<commit_id>",
                                     "type":      "<type>",

rhodecode/lib/vcs/backends/base.py

@@ -221,7 +221,8 b' class MergeResponse(object):'
 
     def asdict(self):
         data = {}
-        for k in ['possible', 'executed', 'merge_ref', 'failure_reason']:
+        for k in ['possible', 'executed', 'merge_ref', 'failure_reason',
+                  'merge_status_message']:
             data[k] = getattr(self, k)
         return data