Properly use origin parameter in porcelain.clone()

The 'origin' parameter in porcelain.clone() wasn't being fully properly
used, as the actual remote was still being set to the default name of
'origin'.  Make the code use the paramter instead at the proper places.

dulwich/porcelain.py

@@ -276,6 +276,7 @@ def clone(source, target=None, bare=False, checkout=None,
     :param checkout: Whether or not to check-out HEAD after cloning
     :param errstream: Optional stream to write progress to
     :param outstream: Optional stream to write progress to (deprecated)
+    :param origin: Name of remote from the repository used to clone
     :return: The new repository
     """
     if outstream is not None:
@@ -323,10 +324,10 @@ def clone(source, target=None, bare=False, checkout=None,
         target_config = r.get_config()
         if not isinstance(source, bytes):
             source = source.encode(DEFAULT_ENCODING)
-        target_config.set((b'remote', b'origin'), b'url', source)
+        target_config.set((b'remote', origin), b'url', source)
         target_config.set(
-            (b'remote', b'origin'), b'fetch',
-            b'+refs/heads/*:refs/remotes/origin/*')
+            (b'remote', origin), b'fetch',
+            b'+refs/heads/*:refs/remotes/' + origin + b'/*')
         target_config.write_to_path()
         if checkout and b"HEAD" in r.refs:
             errstream.write(b'Checking out HEAD\n')