Expand values exposed to the template

Exposed data structure passed to the template is richer
so it now allows the following values to be used in the template:

 {{.ID}}
 {{.Service}}
 {{.Tags}}
 {{.Port}}
 {{.IP}}
 {{.Node}}
 {{.}}

The default {{.}} value remains the same so this change will be
backwards compatible. One could also simulate the default using
the below values in the template:

server {{.Node}}_{{.ID}} {{.IP}}:{{.Port}}