Changed get_nodes method in DeploySelectedNodes

* Added call of TaskHelper.nodes_to_deploy_ha if
  cluster is HA. It is exactly what nodes_to_deploy
  method does in TaskHelper. This method encapsulates
  the logic of appending all cluster controllers
  to nodes_to_deploy if user touches one of them.

DocImpact
Change-Id: Ie1853d49eec0293b760383a467d013dad58f69c1
Closes-Bug: 1386671
Merge "Changed get_nodes method in DeploySelectedNodes"