LU-1308 Additional multihomed nid config fix

LU-1308 Additional multihomed nid config fix

Need to put the new nid addition at the last slot available,
not next after the last.

Change-Id: Icf9d898fba4c6e9c05f085b855a33282ea0d4b47
Signed-off-by: Oleg Drokin <green@whamcloud.com>
Reviewed-on: http://review.whamcloud.com/2599
Reviewed-by: Denis Kondratenko <Denis_Kondratenko@xyratex.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@whamcloud.com>
Tested-by: Hudson
Reviewed-by: Cory Spitz <spitzcor@cray.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>