`gclient-new-workdir.py` is failing on all my machines (Mac, Linux).

It appears to do so while trying to do .a copy in btrfs, which was recently added in Issue 721585.

> gclient-new-workdir.py /Users/lgarron/chromium alt
Traceback (most recent call last):
  File "/Users/lgarron/Code/depot_tools/gclient-new-workdir.py", line 117, in <module>
    sys.exit(main())
  File "/Users/lgarron/Code/depot_tools/gclient-new-workdir.py", line 78, in main
    if try_vol_snapshot(args.repository, args.new_workdir):
  File "/Users/lgarron/Code/depot_tools/gclient-new-workdir.py", line 66, in try_vol_snapshot
    stderr=subprocess.STDOUT)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/subprocess.py", line 535, in check_call
    retcode = call(*popenargs, **kwargs)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/subprocess.py", line 522, in call
    return Popen(*popenargs, **kwargs).wait()
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/subprocess.py", line 710, in __init__
    errread, errwrite)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/subprocess.py", line 1335, in _execute_child
    raise child_exception
OSError: [Errno 2] No such file or directory