Reland "named caches: move instead of symlinking"

appengine/swarming/local_smoke_test.py

 #!/usr/bin/env python
 # Copyright 2014 The LUCI Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0
 # that can be found in the LICENSE file.
 
 """Integration test for the Swarming server, Swarming bot and Swarming client.
 
 It starts both a Swarming server and a Swarming bot and triggers tasks with the
 Swarming client to ensure the system works end to end.
 """
@@ skipping 620 matching lines @@
           ['--secret-bytes-path', tmp, '--', '${ISOLATED_OUTDIR}'],
           expected_summary, {os.path.join('0', 'sekret'): 'foobar\n'})
     finally:
       os.remove(tmp)
 
   def test_local_cache(self):
     # First task creates the cache, second copy the content to the output
     # directory. Each time it's the exact same script.
     script = '\n'.join((
       'import os, shutil, sys',
-      'if not os.path.islink("p/b"):',
-      '  print("p/b is not a symlink")',
-      '  sys.exit(1)',
       'p = "p/b/a.txt"',
       'if not os.path.isfile(p):',
       '  with open(p, "wb") as f:',
       '    f.write("Yo!")',
       'else:',
       '  shutil.copy(p, sys.argv[1])',
       'print "hi"'))
     sizes = sorted([len(script), 200])
     expected_summary = self.gen_expected(
       name=u'cache_first',
@@ skipping 219 matching lines @@
     if bot is not None and bot.poll() is None:
       bot.kill()
       bot.wait()
   finally:
     cleanup(bot, client, servers, failed or verbose, leak)
   return int(failed)
 
 
 if __name__ == '__main__':
   sys.exit(main())