Add support for ETCD SRV name suffix as per description in ETCD dosc:
> The -discovery-srv-name flag additionally configures a suffix to the SRV name that is queried during discovery. Use this flag to differentiate between multiple etcd clusters under the same domain. For example, if discovery-srv=example.com and -discovery-srv-name=foo are set, the following DNS SRV queries are made:
>
> _etcd-server-ssl-foo._tcp.example.com
> _etcd-server-foo._tcp.example.com
All test passes, but not been tested on the live ETCD system yet... Please, take a look and send feedback.
Resolves#2028