SunOS: process nice() is incorrect

[giampaolo]

======================================================================
FAIL: psutil.tests.test_posix.TestProcess.test_nice
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Traceback (most recent call last):
  File "psutil/tests/test_posix.py", line 208, in test_nice
    self.assertEqual(ps_nice, psutil_nice)
AssertionError: 20 != 0

[giampaolo]

So it turns out it's "ps" which is wrong. "ps" retrieves the niceness value from /proc/pid/psinfo which incorrectly returns 20 instead of 0. The real deal is getpriority(2) which correctly returns 0 and psutil relies on it.