Linux: disk_io_counters() is broken on python 3

[giampaolo]

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ERROR: psutil.tests.test_system.TestSystemAPIs.test_disk_io_counters
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Traceback (most recent call last):
  File "/home/giampaolo/svn/psutil/psutil/tests/test_system.py", line 664, in test_disk_io_counters
    ret = psutil.disk_io_counters(perdisk=False)
  File "/home/giampaolo/svn/psutil/psutil/__init__.py", line 2047, in disk_io_counters
    rawdict = _psplatform.disk_io_counters()
  File "/home/giampaolo/svn/psutil/psutil/_pslinux.py", line 1025, in disk_io_counters
    sector_size = get_sector_size(name)
  File "/home/giampaolo/svn/psutil/psutil/_pslinux.py", line 248, in get_sector_size
    with open(b"/sys/block/%s/queue/hw_sector_size" % partition) as f:
TypeError: %b requires bytes, or an object that implements __bytes__, not 'str'