Add host to cluster

[rjrudin]

Combo of calling http://docs.marklogic.com/REST/GET/admin/v1/server-config and then http://docs.marklogic.com/REST/POST/admin/v1/cluster-config .

Simplest way of doing this would be:

gradle -PmlHost=address -PclusterHost=address mlAddHost

Where mlHost is the address of the host we want to add to a cluster (so the GET call is made to it). And clusterHost is the address of a host in the cluster we want to join (and so the POST call is made to it).

Will need to wait for a restart in case a 202 is returned.

Should also support optional parameters of "group" and "zone". "group" seems to be required and should default to "mlGroup".

Most of this will work be done in ml-app-deployer.