spec:system - Change VM IP to fix virtualbox/vagrant error

Closes-bug: #1262401
Change-Id: I1cf022cfd3de813d08c8fbf5c8321f9b625fb4cf
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>