Don't use single item list for node in heat
Let's not use a single item list for node.
lbaasversion: lbaasv2
- '{pipeline}-tempest-dsvm-heat{special}-{node}{suffix}':
pipeline: gate
- node:
- - ubuntu-xenial
+ node: ubuntu-xenial
special: '-identity-v3-only'
suffix: '-nv'
branch-override: default
