Now Magnums onlys has one server group for all master and worker nodes
per cluster, which is not very flexible for small cloud scale. For a
3+ master clusters, it's easily meeting the capacity when using hard
anti-affinity policy. This patch is proposing one server group for each
master and worker nodes group to have better flexibility.
story: 2004195
Change-Id: If11ba863a2aa538efe1e3e850084bdd33afd27d2