LU-582 test: fix bug in get_ost_param in sanity.sh

LU-582 test: fix bug in get_ost_param in sanity.sh

in get_ost_param(), the ouput should be gl_sum, which is
the sum of 'gl' in all OSS.

Signed-off-by: Hongchao Zhang <hongchao.zhang@whamcloud.com>
Change-Id: I51d3aa591c3ca875f8a559974cf05d250b0c032a
Reviewed-on: http://review.whamcloud.com/3693
Reviewed-by: Jian Yu <jian.yu@intel.com>
Tested-by: Jian Yu <jian.yu@intel.com>
Tested-by: Hudson
Reviewed-by: Fan Yong <fan.yong@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>