$(ALPHA_FEATURE_GATES) on gcloud-terraform-install (#1663)
$(ALPHA_FEATURE_GATES) on gcloud-terraform-install (#1663)

Minor cleanup to use the feature gate variable in the Terraform make
commands.
googleforgames/agones,googleforgames/agones,googleforgames/agones,googleforgames/agones,googleforgames/agones,googleforgames/agones,googleforgames/agones,googleforgames/agones