lfs: convert hexdigest to bytes using sysbytes

lfs: convert hexdigest to bytes using sysbytes

Differential Revision: https://phab.mercurial-scm.org/D2568

--- a/hgext/lfs/wrapper.py	Fri Mar 02 11:07:25 2018 -0500
+++ b/hgext/lfs/wrapper.py	Fri Mar 02 11:07:42 2018 -0500
@@ -10,7 +10,7 @@
 import hashlib
 
 from mercurial.i18n import _
-from mercurial.node import bin, nullid, short
+from mercurial.node import bin, hex, nullid, short
 
 from mercurial import (
     error,
@@ -85,7 +85,7 @@
         text = text[offset:]
 
     # git-lfs only supports sha256
-    oid = hashlib.sha256(text).hexdigest()
+    oid = hex(hashlib.sha256(text).digest())
     self.opener.lfslocalblobstore.write(oid, text)
 
     # replace contents with metadata