credential incorrectly processes tenant/project id

[wallyworld]

It's possible to have a novarc file with a keystone v3 set of credential attributes like this:

export OS_USERNAME=fred
export OS_PASSWORD=secret
export OS_USER_DOMAIN_NAME=user
export OS_PROJECT_NAME=vinu
export OS_PROJECT_ID=cab03d5e990e438dae80aedb58ffde77
export OS_PROJECT_DOMAIN_NAME=user

These will be parsed into a credential where the "TenantName" attribute is set to "cab03d5e990e438dae80aedb58ffde77". But that value is the tenant id, not name. And then when we go to authenticate, we do this:

auth.Auth.Scope = &v3AuthScope{
Project: &v3AuthProject{
Domain: &v3AuthDomain{
Name: projectDomain,
},
Name: creds.TenantName,
},
}

The auth v3AuthProject struct does have an ID field and that's what should be set in this case.

The identity.Credentials struct could gain a TenantId field and we use that if set. But maybe we can simply not use the id at all because:

1. We only use Name in v3AuthDomain (we ignore ID)
2. I tested auth with v3AuthProject.Name = "" and it worked

So we could start by simply modifying the CredentialsFromEnv() function and associated validation to not set TenantName from OS_TENANT_ID etc.