LU-6090 lnet: save errno between function calls

LU-6090 lnet: save errno between function calls

errno can be overwritten by functions like snprintf even if
it succeeded, so save the errno when needed.

Signed-off-by: Amir Shehata <amir.shehata@intel.com>
Change-Id: I9a47267851f7c102727f8653a3a3727047f33186
Reviewed-on: http://review.whamcloud.com/15783
Tested-by: Jenkins
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>