This patch introduces the following changes.
1. benchmark-operator is deployed during browbeat installation if install_e2e_benchmarking
is set to true in group_vars/all.yml. This is because the same operator can be used for
multiple Rally iterations.
2. A rally plugin to run kube-burner workloads has been created.
Change-Id: I4fb67c4e986a8be589cf1eca615b2bb2748cba55