First step in removing references to instance_types. Rename instnace_types.py
and update references to it. We currently use instance_type and flavor as
synonyms, to reduce confusion we are picking one. We are going with our own
terminology, flavors.
renamed: nova/compute/instance_types.py -> nova/compute/flavors.py
Partially implements bp flavor-instance-type-dedup
Change-Id: I9dc04cf311aa8813be4f5329f23729d2c43cae6d