Use proxy address for default check

[lkysow]

When a sidecar proxy is registered, a check is automatically added.
Previously, the address this check used was the underlying service's
address instead of the proxy's address, even though the check is testing
if the proxy is up.

This worked in most cases because the proxy ran on the same IP as the
underlying service but it's not guaranteed and so the proper default
address should be the proxy's address.

The docs say:

By default we add a TCP check on the local address and port for the proxy, and a service alias check for the parent service. If either check or checks fields are set, only the provided checks are registered.

Which is now correct but previously was incorrect.

Testing & Reproduction steps

• Tested via unit tests

services {
  name = "s1"
  port = 8181
  connect {
    sidecar_service {
      address = "255.255.255.255"
      proxy {
      }
    }
  }
}

consul agent -dev -config-file service.hcl

curl localhost:8500/v1/agent/checks                                                                                                           ⎈ kind-kind
{
    "service:s1-sidecar-proxy:1": {
        "Node": "Lukes-MacBook-Pro.local",
        "CheckID": "service:s1-sidecar-proxy:1",
        "Name": "Connect Sidecar Listening",
        "Status": "critical",
        "Notes": "",
        "Output": "dial tcp 255.255.255.255:21000: connect: address family not supported by protocol family",
...

This proves it's using the correct address. Previously it would use 127.0.0.1, the address of the service instance.

PR Checklist

• updated test coverage
• not a security concern

[lkysow]

I removed the comments here because the first one:

// Setup default check if none given

Is already commented where this function is called and the second one is now commented where we pass in the address.