allow multiline returns from docker for mac

Nothing actually specifies the number of lines the docker api returns,
so we need to allow for more than one line to be returned which this
specfic docker returner does

salt/modules/dockerng.py

@@ -559,6 +559,17 @@ def __virtual__():
     return (False, 'Docker module could not get imported')
 
 
+class DockerJSONDecoder(json.JSONDecoder):
+    def decode(self, s, _w=None):
+        objs = []
+        for line in s.splitlines():
+            if not line:
+                continue
+            obj, _ = self.raw_decode(line)
+            objs.append(obj)
+        return objs
+
+
 def _get_docker_py_versioninfo():
     '''
     Returns the version_info tuple from docker-py
@@ -3459,7 +3470,9 @@ def build(path=None,
             .format(image)
         )
 
-    stream_data = [json.loads(x) for x in response]
+    stream_data = []
+    for line in response:
+        stream_data.extend(json.loads(line, cls=DockerJSONDecoder))
     errors = []
     # Iterate through API response and collect information
     for item in stream_data: