test mon address are now s/10.11.12.1/10.11.12.3/

Because .nodeset.yml was changed in the same way, the corresponding
rspec:system test must also be changed.

Change-Id: Id9aad194c9c4a323c3dea4bba71e3c94f606aa6c
Signed-off-by: Loic Dachary <loic@dachary.org>