VDSM periodically logs Worker blocked warning messages in vdsm.virt.sampling.HostMonitor

Issue

• No apparent problem is seen, but VDSM logs are full of warnings regarding blocked workers doing HostMonitor
• VDSM logs are filled with the following warning:

WARN Worker blocked: <Worker name=periodic/82 running <Task <Operation action=<vdsm.virt.sampling.HostMonitor object at 0x7f94e443fe50> at 0x7f94e443fe90> timeout=15,
      File: "/usr/lib64/python2.7/threading.py", line 785, in __bootstrap
        self.__bootstrap_inner()
      File: "/usr/lib64/python2.7/threading.py", line 812, in __bootstrap_inner
        self.run()
      File: "/usr/lib64/python2.7/threading.py", line 765, in run
        self.__target(*self.__args, **self.__kwargs)
      File: "/usr/lib/python2.7/site-packages/vdsm/common/concurrent.py", line 194, in run
        ret = func(*args, **kwargs)
      File: "/usr/lib/python2.7/site-packages/vdsm/executor.py", line 301, in _run
        self._execute_task()
      File: "/usr/lib/python2.7/site-packages/vdsm/executor.py", line 315, in _execute_task
        task()
      File: "/usr/lib/python2.7/site-packages/vdsm/executor.py", line 391, in __call__
        self._callable()
      File: "/usr/lib/python2.7/site-packages/vdsm/virt/periodic.py", line 220, in __call__
        self._func()
      File: "/usr/lib/python2.7/site-packages/vdsm/virt/sampling.py", line 576, in __call__
        sample = HostSample(self._pid)
      File: "/usr/lib/python2.7/site-packages/vdsm/virt/sampling.py", line 240, in __init__
        self.interfaces = _get_interfaces_and_samples()
      File: "/usr/lib/python2.7/site-packages/vdsm/virt/sampling.py", line 200, in _get_interfaces_and_samples
        for link in ipwrapper.getLinks():
      File: "/usr/lib/python2.7/site-packages/vdsm/network/ipwrapper.py", line 267, in getLinks
        in six.viewitems(dpdk.get_dpdk_devices()))
      File: "/usr/lib/python2.7/site-packages/vdsm/network/link/dpdk.py", line 47, in get_dpdk_devices
        dpdk_devices = _get_dpdk_devices()
      File: "/usr/lib/python2.7/site-packages/vdsm/common/cache.py", line 41, in __call__
        value = self.func(*args)
      File: "/usr/lib/python2.7/site-packages/vdsm/network/link/dpdk.py", line 111, in _get_dpdk_devices
        devices = _lshw_command()
      File: "/usr/lib/python2.7/site-packages/vdsm/network/link/dpdk.py", line 123, in _lshw_command
        rc, out, err = cmd.exec_sync(['lshw', '-json'] + filterout_cmd)
      File: "/usr/lib/python2.7/site-packages/vdsm/network/cmd.py", line 38, in exec_sync
        retcode, out, err = exec_sync_bytes(cmds)
      File: "/usr/lib/python2.7/site-packages/vdsm/common/cmdutils.py", line 156, in exec_cmd
        out, err = p.communicate()
      File: "/usr/lib64/python2.7/site-packages/subprocess32.py", line 924, in communicate
        stdout, stderr = self._communicate(input, endtime, timeout)
      File: "/usr/lib64/python2.7/site-packages/subprocess32.py", line 1706, in _communicate
        orig_timeout)
      File: "/usr/lib64/python2.7/site-packages/subprocess32.py", line 1779, in _communicate_with_poll
        ready = poller.poll(self._remaining_time(endtime))