In the other places subnodes is a group and there is a node called
secondary put in to it. It shouldn't matter, but as centos-7-2-node and
ubuntu-xenial-2-node are defined differently it could cause someone to
be confused or think there is a reason for the divergence.
Change-Id: Icd28da7c1c20b605841cd27f4f656e4b8f812fee
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