Builder for `ApiService`

[elazarl]

When creating a new service your code have to go like

ApiService svc = new ApiService();
svc.setClusterRef(new ClusterRef(cluster.getName()));
svc.setName("hdfs");
svc.setType("HDFS");
List<ApiRoles> roles = new ArrayList<>();
svc.setRoles(roles);
ApiRole role = new ApiRole();
role.setName("mynamenode");
role.setType("NAMENODE");
roles.add(role);

etc.

It'll be nicer to have a nicer API like

ApiServiceBuilder.newHdfs("myhdfs1", cluster).
    withRole(ApiRoleBuilder.newNameNode("mynamenode", host2)).
    withRole(ApiRoleBuilder.newDataNode("myDataNode", host1)).
    build();

Will you accept pull requests? I'm having something I can make a pull request from.