Tezt/Cloud: additional configuration step

In order to deploy Tezt-cloud scenarios, several engineers reported that they had to run the following command that is not described in the current Tezt-cloud documentation, and which is supposed to be already included in the current scripts.
This can be investigated so that it's fixed permanently and transparent for the Tezt-cloud user.

terraform  '-chdir=tezt/lib_cloud/terraform/vm' init