Nomad Consul connect "dial tcp: lookup unix: Temporary failure in name resolution"

Nomad v0.11.1 (b43457070037800fcc8442c8ff095ff4005dab33)

I've run into the following problem:

```
May 15 11:18:25 ip-10-1-89-245 nomad[39744]: 2020-05-15T11:18:25.141Z [ERROR] client.alloc_runner.runner_hook: error connecting to grpc: alloc_id=0de4add2-2b81-fed5-7cd6-a05a168e26d6 error="dial tcp: lookup unix: Temporary failure in name resolution" dest=unix:8502
```

Example Consul client config:

```
# Support for Consul Connect
ports {
"grpc" = 8502
}

connect {
enabled = true
}

addresses {
http = "unix:///tmp/consul.sock"
grpc = "unix:///tmp/consul-grpc.sock"
}
```

Example Nomad config:
```
consul {
address = "unix:///tmp/consul.sock"
}
```

From my understanding, to enable GRPC in Consul I must define a port for it.

Does Nomad support GRPC UNIX socket?

Start by tracing Nomad's Consul Connect gRPC address handling using the provided Consul and Nomad configurations, then reproduce the reported unix-socket resolution error. Done means determining whether gRPC Unix sockets are supported and, if a change is needed, defining the required behavior and validating it against this configuration.

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