handle binary stream from urllib.request.urlopen

Python 3 returns bytes by default with urlopen.  Adjust our code to
handle that scenario and decode as necessary.

Bug: https://crbug.com/gerrit/10418
Change-Id: Icf4cd80e7ef92d71a3eefbc6113f1ba11c32eebc
diff --git a/repo b/repo
index aa357a2..ce42ad0 100755
--- a/repo
+++ b/repo
@@ -583,7 +583,7 @@
         print('Get %s' % url, file=sys.stderr)
       while True:
         buf = r.read(8192)
-        if buf == '':
+        if not buf:
           return True
         dest.write(buf)
     finally: