Configurable timeout on build(), defaults to None

Many commands used in Dockerfiles hang for an extended period of time
without producing any output, which will result in a socket timeout.
Accordingly, it makes sense for build() to specify no timeout by
default.

docker/client.py

@@ -308,7 +308,7 @@ class Client(requests.Session):
             u, None, params=self._attach_params(params), stream=True))
 
     def build(self, path=None, tag=None, quiet=False, fileobj=None,
-              nocache=False, rm=False, stream=False):
+              nocache=False, rm=False, stream=False, timeout=None):
         remote = context = headers = None
         if path is None and fileobj is None:
             raise Exception("Either path or fileobj needs to be provided.")
@@ -332,7 +332,7 @@ class Client(requests.Session):
             headers = {'Content-Type': 'application/tar'}
 
         response = self._post(
-            u, data=context, params=params, headers=headers, stream=stream
+            u, data=context, params=params, headers=headers, stream=stream, timeout=timeout
         )
 
         if context is not None: