The Redis client allows specifying connection options in several ways, with
sensible defaults. The following all translate into `127.0.0.1:6379`:

```js
createClient('redis://127.0.0.1:6379');
createClient({ host: '127.0.0.1', port: NaN });
createClient({})
createClient()
```

Redis somewhat normalises these separate options into its `options` member, and
stores the properties it uses to connect to the server in
`connection_options`. Examples of the difference between the two in the examples
preceding (slightly redacted for ease of reading):

```js
createClient('redis://127.0.0.1:6379');
// options = { port: '6379', host: '127.0.0.1' }
// connection_options = { port: 6379, host: '127.0.0.1', family: 4 }

createClient({ host: '127.0.0.1', port: NaN });
// options = { host: '127.0.0.1', port: NaN }
// connection_options = { port: 6379, host: '127.0.0.1', family: 4 }

createClient()
// options = { host: undefined }
// connection_options = { port: 6379, host: '127.0.0.1', family: 4 }
```

The instrumentation before this commit looks at the `options` property, which
contains caller-supplied values before they're fully normalised and smoothed
over by Redis. This means that for these weird cases, the instrumentation would
populate `NET_PEER_NAME` and `NET_PEER_PORT` with erroneous values.

This commit has the instrumentation the values the Redis client uses to connect
to the server, mirroring actual use.