couchbase analytics-link-setup doesn't work remotely with node name of 127.0.0.1

Problem
Single node clusters are often configured with a node name of 127.0.0.1. When couchbase-cli is executed remotely it will resolve the host:port for specific services (e.g. CBAS_SERVICE), in this case that will be 127.0.0.1 and as a result it will fail.

This breaks configuring analytics links on single node clusters with a name of 127.0.0.1.

Suggested fix
The address used to contact the cluster should be used on missing hostname and not 127.0.0.1, which it looks like is available as used_host in this function.

Steps to reproduce
1. Create single-node cluster, configure w/ KV + Analytics- ensure node name is '127.0.0.1' -
2. From a separate machine that does not Couchbase w/ Analytics running, run

$ couchbase-cli analytics-link-setup -c <server created in step 1> -u couchbase -p couchbase --list

ERROR: Unable to connect to host at http://<server created in step 1>:8091: HTTPConnectionPool(host='127.0.0.1', port=8095): Max retries exceeded with url: /analytics/link (Caused by NewConnectionError('<requests.packages.urllib3.connection.HTTPConnection object at 0x7f1f454ee3c8>: Failed to establish a new connection: [Errno 111] Connection refused'))

Workaround
Define an external address on the node prior to executing the analytics-link-setup CLI command.