wp*: dbpass is shown in plaintext in `terraform show` or `terraform state show`

[pecio]

In the openstack_compute_instance_v2 resources, metadata parameter correctly censors db_pass but all_metadata does not:

    all_metadata        = {
        "db_addr" = "192.168.200.232"
        "db_name" = "wp"
        "db_pass" = "-FVP$CtJaurSI5!d"
        "db_user" = "wp"
    }
.
.
.
    metadata            = {
        "db_addr" = "192.168.200.232"
        "db_name" = "wp"
        "db_pass" = (sensitive)
        "db_user" = "wp"
    }

Note that, whatever we do, tfstate will keep it plaintext but this is always so with Terraform and sensitive data.

[pecio]

My original idea was to use OpenStack Barbican to store the password, but there is no concept of "Service Accounts" or "Instance Roles" in OpenStack, and neither are API endpoints easily discoverable from the Nova instances, except for the metadata endpoint http://169.254.169.254/.

[pecio]

After #11, passwords are shown in rendered templates instead of instance metadata, but the problem persists.