LU-1850 test: remount client if replay-vbr fails

LU-1850 test: remount client if replay-vbr fails

Remount client lustre if checkstat fails to make sure
the following tests running in a healthy environment

Change-Id: I764e83ee31d8cc19d79632e805a6e75225e67adf
Signed-off-by: sarah <sarah@whamcloud.com>
Reviewed-on: http://review.whamcloud.com/4063
Tested-by: Hudson
Reviewed-by: Yu Jian <yujian@whamcloud.com>
Reviewed-by: Niu Yawei <niu@whamcloud.com>
Reviewed-by: Li Wei <liwei@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>