Validate mappings targets

[concaf]

#23 was caused because we never knew if the ObjectMeta that we referenced existed in the Kubernetes Open API definitions.We need to add a check before/after the final mappings are generated to see if the target actually exists in the Kubernetes or OpenShift Open API definitions.

CC: @surajssd

[surajssd]

if it does not exist we fail so that we know we are not using outdated refs in types.go