This patch ensures that the default flavor is used when the flavor
parameter (Overcloud{{role.name}}Flavor) is not explicitly defined
in deployment templates and plan, to emulate the behavior in tht
to pick up the defalt flavor to deploy baremetal instances.
Closes-Bug: #1901472
Change-Id: I6970a7fc294305d4fe6ad43b9c2e29090a1ecb37