Rename instance_type to flavor in baremetal virt driver

Goes through the baremetal virt driver and associated classes and tests
and renames instance_type to flavor. This patch does not handle renaming
instance_type in nova.test.utils or the instance_type_id column in the
instance db model so those parts are left unchanged here.

DocImpact: Renames the 'instance_type_extra_specs' option in the
baremetal group to 'flavor_extra_specs'.

Part of blueprint flavor-instance-type-dedup

Change-Id: I4405464aea2b2e2142ed1207fb9c25ed9e863cb0
Merge "Rename instance_type to flavor in baremetal virt driver"