fix(vault): fix vault service fqdn

[gbloquel]

When the task Check vault API avalability, the url returned is bad and the task fails.

Below the vars

• hs_vault_external_url=https://hashistack.hashistack.example.com
• hs_vault_service_fqdn=hashistack.hashistack.example.com
• hs_vault_cluster_name=hashistack
• hs_vault_domain=hashistack.example.com

This PR fixes the var hs_vault_service_fqdn .

[aurelienmaury]

If we are talking about defaults, the described cas implies that:

• the variable hs_workspace is hashistack
• the variable hs_parent_domain is example.org
• the variable hs_vault_cluster_name is at its default value of the same as hs_workspace

To avoid this duplication, you have to specify either your hs_vault_cluster_name or your desired hs_vault_service_fqdn to create a prettier URL.

As, most of the time, you won't desire having the vault service responding on the root of your public domain, I can't accept this modification, sorry.