This PR fixes the Nomad Object Namespace <-> Consul ACL Token relationship
check when using Consul OSS (or Consul ENT without namespace support).
Nomad v1.1.0 introduced a regression where Nomad would fail the validation
when submitting Connect jobs and allow_unauthenticated set to true, with
Consul OSS - because it would do the namespace check against the Consul ACL
token assuming the "default" namespace, which does not work because Consul OSS
does not have namespaces.
Instead of making the bad assumption, expand the namespace check to handle
each special case explicitly.
Fixes#10718
Florian Apolloner