[scenarios] Differentiate virtual node roles

[scenarios] Differentiate virtual node roles

Split scenario yaml definitions for virtual.nodes based on node
role ('infra', 'control' or 'compute'), to be leveraged later to
contruct node lists based on said role.

This moves the responsability of filtering node names in scenario
files (based on 'virtual' or 'baremetal' type) to xdf_data.sh.j2,
simplifying scenario templates.

By keeping all nodes (both virtual and baremetal) in scenario files,
we can later determine the role (and implicitly the hostname) for a
MaaS-managed node based on its index in the virtual.nodes.control
structure.

JIRA: FUEL-382

Change-Id: I1f83a307631f4166ee1c57ef598c44876b962f97
Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>