Added eligilie_* methods for cloud provisioning to automate

Added eligible_* methods to miq_ae_service_miq_provision_cloud model
Derive Amazon and Openstack models from the cloud model.
Refactor miq_provision_mixin to support cloud and infra methods.

https://bugzilla.redhat.com/show_bug.cgi?id=1029654
Added tests for cloud provisioning models in automate.

https://bugzilla.redhat.com/show_bug.cgi?id=1029654
Added eligible_tenants to openstack automate provisioning

Added cloud_tenant service model and factory.

https://bugzilla.redhat.com/show_bug.cgi?id=1029654