Description of problem:

error looks as follows:

Traceback (most recent call last):
  File "/usr/share/vdsm/utils.py", line 389, in collect
    statsFunction()
  File "/usr/share/vdsm/utils.py", line 266, in __call__
    retValue = self._function(*args, **kwargs)
  File "/usr/share/vdsm/libvirtvm.py", line 157, in _sampleDiskLatency
    stats = _blockstatsParses(out)
  File "/usr/share/vdsm/libvirtvm.py", line 144, in _blockstatsParses
    'flush_op':devStats['flush_operations'],
KeyError: 'flush_operations'

problem is in the following function:
------------------------------------------------------------------------------
def _sampleDiskLatency(self):
        if not self._vm._volumesPrepared:
            # Avoid queries from storage during recovery process
            return

        def _blockstatsParses(devList):
            # The json output looks like:
            # {u'return': [{u'device': u'drive-ide0-0-0',
            #               u'stats': {u'rd_operations': 0, u'flush_total_time_ns': 0, u'wr_highest_offset': 0, u'rd_total_time_ns': 0,
            #                          u'rd_bytes': 0, u'wr_total_time_ns': 0, u'flush_operations': 0, u'wr_operations': 0, u'wr_bytes':0},
            #               u'parent': {u'stats': {u'rd_operations': 0, u'flush_total_time_ns': 0, u'wr_highest_offset': 0,
            #                                      u'rd_total_time_ns': 0, u'rd_bytes': 0, u'wr_total_time_ns': 0, u'flush_operations': 0,
            #                                      u'wr_operations': 0, u'wr_bytes': 0}
            #                          }
            #               },
            #               {u'device': u'drive-ide0-1-0',
            #                u'stats': {u'rd_operations': 0, u'flush_total_time_ns': 0, u'wr_highest_offset': 0, u'rd_total_time_ns': 0,
            #                           u'rd_bytes': 0, u'wr_total_time_ns': 0, u'flush_operations': 0, u'wr_operations': 0, u'wr_bytes': 0}
            #               }],
            #  u'id': u'libvirt-9'}
            stats = {}
            self._log.debug('#### print device list: %s', devList)
            for item in devList['return']:
                fullDevName = item['device']
                alias = fullDevName[len('drive-'):].strip()
                devStats = item['stats']
                stats[alias] = {'rd_op':devStats['rd_operations'],
                                'wr_op':devStats['wr_operations'],
                                'flush_op':devStats['flush_operations'],
                                'rd_total_time_ns':devStats['rd_total_time_ns'],
                                'wr_total_time_ns':devStats['wr_total_time_ns'],
                                'flush_total_time_ns':devStats['flush_total_time_ns']}

------------------------------------------------------------------------------

from printing I added, i noticed that devList is missing some params function relies on; hence failing on keyError:

devList['return'] printing: 

{u'wr_highest_offset': 3183537664, u'rd_bytes': 70507520, u'wr_operations': 189, u'rd_operations': 3402, u'wr_bytes': 1369088}

git commit: 82969b3b5ca2f9487ea56485fafd843b21d4f447