LU-2087 ofd: refresh blocks in lvb from rpc

LU-2087 ofd: refresh blocks in lvb from rpc

like obdfilter does. let blocks only increase unless
specified with the flag. this should fix sanityn/4.

Signed-off-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Change-Id: I85bf45f091637faf39c65e0acf331f37dab7af7e
Reviewed-on: http://review.whamcloud.com/4180
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Hudson
Reviewed-by: wangdi <di.wang@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Johann Lombardi <johann.lombardi@intel.com>