LU-1668 tests: fix for conf-sanity 53_a & 53_b

LU-1668 tests: fix for conf-sanity 53_a & 53_b

conf-sanity 53_a & 53_b are using local cpt number as increment or
decrement of threads number which is wrong, they should use cpt
number from target server.

Test-Parameters: nettype=o2ib
Signed-off-by: Liang Zhen <liang@whamcloud.com>
Change-Id: Ief25ecfefc291decd6e72067b1363942a5871f81
Reviewed-on: http://review.whamcloud.com/3595
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: wangdi <di.wang@whamcloud.com>
Reviewed-by: James Simmons <uja.ornl@gmail.com>