Begin incorporating Python unit tests into build

We now build a separate APE binary for each test so they can run in
parallel. We've got 148 tests running fast and stable so far.

third_party/python/Lib/test/test_bytes.py

@@ -9,6 +9,7 @@ import os
 import re
 import sys
 import copy
+import _cosmo
 import functools
 import pickle
 import tempfile
@@ -846,6 +847,8 @@ class BytesTest(BaseBytesTest, unittest.TestCase):
         with self.assertRaisesRegex(TypeError, msg):
             b'python'['a']
 
+    @unittest.skipIf(_cosmo.MODE in ('tiny', 'rel'),
+                     "fails on missing .py file in rel omed")
     def test_buffer_is_readonly(self):
         fd = os.open(__file__, os.O_RDONLY)
         with open(fd, "rb", buffering=0) as f: