Consul watch ignores HTTP API Options on command line

#### Overview of the Issue

`consul watch` command doesn't pass down HTTP flags (args) down to watch plan.

https://github.com/hashicorp/consul/blob/master/command/watch/watch.go#L252 passes a nil config down which causes the watch plan to re-create a NewClient with mostly default options, while the HTTP options from https://github.com/hashicorp/consul/blob/master/command/watch/watch.go#L162 get discarded.

Using environment variables for the HTTP options still works since the new re-created Client in plan.go will parse those upon creation.

#### Reproduction Steps

Run consul with a self signed certificate and a custom CA file.

```
~# consul watch -http-addr https://consul-server-addr:8443 -type nodes
Error querying Consul agent: Get https://consul-server-addr:8443/v1/agent/self: x509: certificate signed by unknown authority

~# consul watch -ca-file /etc/consul.d/ca.crt -http-addr https://consul-server-addr:8443 -type nodes
2019/12/11 00:16:14 [ERR] consul.watch: Watch (type: nodes) errored: Get https://consul-server-addr:8443/v1/catalog/nodes: x509: certificate signed by unknown authority, retry in 5s
^C

~# env CONSUL_CACERT=/etc/consul.d/ca.crt consul watch -http-addr https://consul-server-addr:8443 -type nodes
[
{
"ID": "f75216c7-d78a-5757-xxxx-346e0a4b64b8",
...
```