Bug 1547730 - Fix b''.join(rand.choice(bytestring)..) to use bytes() constructor instead r=#build

Differential Revision: https://phabricator.services.mozilla.com/D28107

--HG--
extra : rebase_source : b630c75e57f967d70704dcffbbac0fa1aeb4e627
extra : intermediate-source : 59159c8d965b9f1fe7a8d7ac498f1e56489e578a
extra : source : 915a3ded66d8f598a8c6541dbbf842e5f12fc7e2

python/mozbuild/mozpack/test/test_files.py

@@ -163,9 +163,8 @@ class TestDest(TestWithTmpDir):
         self.assertEqual(dest.read(), 'qux')
 
 
-rand = b''.join(random.choice(
-    b'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ')
-                for i in six.moves.xrange(131597))
+rand = bytes(random.choice(b'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ')
+             for i in six.moves.xrange(131597))
 samples = [
     b'',
     b'test',