Refactor validate_resource_definitions()
Refactor validate_resource_definitions()

We moved validate_resource_definitions() to template_common.py
for hot/cfn in Commit ed08e4f676d4512209937289e2068b62fb8591a0,
but then the Change I8fda1380504d1d8b1e96649bf20b86d6309fdeca
overwrote the method to validate the 'external_id', in fact
we could overwrite validate_resource_definition().

Change-Id: I1c6ce382d4d968602504f2e79f903c6d521cf288

openstack/heat,openstack/heat,cwolferh/heat-scratch,noironetworks/heat,noironetworks/heat,cwolferh/heat-scratch