Allow device ID to be equal to 0 on OpenBSD

[andrewkroh]

The OpenBSD build is failing on this test assertion.

[andrewkroh]

I added a second commit to fix these failures.

. /home/vagrant/go/src/github.com/elastic/beats/filebeat/build/python-env/bin/activate; nosetests -w tests/system --processes=4 --process-timeout=90 -a '!integration'
.......S...........................................E...E.......S........
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ERROR: In case a prospector is defined but doesn't contain any paths, prospector must return error which
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Traceback (most recent call last):
  File "/home/vagrant/go/src/github.com/elastic/beats/filebeat/tests/system/test_prospector.py", line 277, in test_no_paths_defined
    filebeat.check_kill_and_wait(exit_code=1)
  File "../../../libbeat/tests/system/beat/beat.py", line 79, in check_kill_and_wait
    self.kill()
  File "../../../libbeat/tests/system/beat/beat.py", line 60, in kill
    self.proc.terminate()
  File "/usr/local/lib/python2.7/subprocess.py", line 1559, in terminate
    self.send_signal(signal.SIGTERM)
  File "/usr/local/lib/python2.7/subprocess.py", line 1554, in send_signal
    os.kill(self.pid, sig)
OSError: [Errno 3] No such process

======================================================================
ERROR: In case no prospectors are defined, filebeat must shut down and report an error
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Traceback (most recent call last):
  File "/home/vagrant/go/src/github.com/elastic/beats/filebeat/tests/system/test_prospector.py", line 254, in test_shutdown_no_prospectors
    filebeat.check_kill_and_wait(exit_code=1)
  File "../../../libbeat/tests/system/beat/beat.py", line 79, in check_kill_and_wait
    self.kill()
  File "../../../libbeat/tests/system/beat/beat.py", line 60, in kill
    self.proc.terminate()
  File "/usr/local/lib/python2.7/subprocess.py", line 1559, in terminate
    self.send_signal(signal.SIGTERM)
  File "/usr/local/lib/python2.7/subprocess.py", line 1554, in send_signal
    os.kill(self.pid, sig)
OSError: [Errno 3] No such process

----------------------------------------------------------------------
Ran 72 tests in 36.834s

FAILED (SKIP=2, errors=2)