CLI: acl policy read -format=json output is not json when policy is not found

#### Overview of the Issue

`acl policy read` prints non-json for `--format=json`, whent the matching record is not found (both for `-name` and `id` option)

The output must be in json as the option is given.

Not sure how other "wrapping" command works - it may returns the custom struct (like output of `vault operator init -status`) - or bad response from the `/v1/acl/policies` endpoint.

(Related: #5904)

#### Reproduction Steps

1. Create a cluster with ACL enabled
1. run `consul acl policy read -format=json` with `-name` or `-id` option with non-existing value

Client output:

With `-name`

```
Error determining policy ID: Unexpected response code: 403 (ACL not found)
```

With `-id`

```
Error reading policy "d271fdd0-6740-4e71-bf6e-519f4439b660": Unexpected response code: 403 (ACL not found)
```

### Consul info for both Client and Server

Both server and client:

```
consul -version
Consul v1.9.1
Revision ca5c38943
```

### Operating system and Environment details

macOS

### Log Fragments

Server:

```
[ERROR] agent.http: Request error: method=GET url=/v1/acl/policies from=127.0.0.1:51947 error="ACL not found"
[DEBUG] agent.http: Request finished: method=GET url=/v1/acl/policies from=127.0.0.1:51947 latency=108.681µs
```