deployment planners plan per clusters not hosts

Concentration or Dispersion granularity is at the Cluster level and not
at the host level. So correcting the test to ensure

a. concentrated planner puts the VMs in same cluster
b. dispersed planner puts the Vms in diff't clusters

Signed-off-by: Prasanna Santhanam <tsp@apache.org>
Test should find Routing hosts not specific hypervisor_type

Bug in listing hosts that can be used for deploying VMs. Use Routing
hosts to identify hosts regardless of hypervisor_type.

Signed-off-by: Prasanna Santhanam <tsp@apache.org>