LU-5718 lnet: add offset for selftest brw

LU-5718 lnet: add offset for selftest brw

In current lnet selftest, both client and server side bulk have
no offset and we can only test page aligned IO, this patch changed
this:

- user can set brw offset by lst add_test ... brw off=OFFSET ...
- offset is only effective on client side so far
- to simply implementation, offset needs to be eight bytes aligned

Signed-off-by: Liang Zhen <liang.zhen@intel.com>
Change-Id: I34690d2c8fbb627b827291afcd46d7aa59831a3f
Reviewed-on: http://review.whamcloud.com/12496
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Doug Oucharek <doug.s.oucharek@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>