ocp4-cluster: use include_role because gcp role don't exist yet (#1276)

This commit, if applied, fixed the following error:

ERROR! the role 'infra-gcp-create-inventory' was not found in /home/travis/build/redhat-cop/agnosticd/ansible/configs/ocp4-cluster/roles:/home/travis/build/redhat-cop/agnosticd/roles:/home/travis/build/redhat-cop/agnosticd/ansible/roles:/home/travis/build/redhat-cop/agnosticd/ansible/configs/ocp4-cluster
The error appears to be in '/home/travis/build/redhat-cop/agnosticd/ansible/configs/ocp4-cluster/destroy_env.yml': line 64, column 13