set vault license for enterprise tests (#240)

Since hashicorp/vault-enterprise:latest now requires a license to do
anything, we need to set $VAULT_LICENSE when provisioning the
enterprise docker container.

docker-compose.yml

@@ -12,6 +12,7 @@ services:
     image: hashicorp/vault-enterprise:latest
     environment:
       VAULT_DEV_ROOT_TOKEN_ID: testtoken
+      VAULT_LICENSE: ${VAULT_LICENSE_CI}
     ports:
       - 8200:8200
     privileged: true