non-spotify specific master resolution

* Remove spotify specific srv format and domain.
* Make the srv format configurable via a HELIOS_SRV_FORMAT environment
  variable.

dnsjava uses the dns search list in /etc/resolv.conf, so users in
environments with correctly configures dns search domains will not need
to enter fully qualified helios domain names during normal use.
```
The format of the SRV RR

   Here is the format of the SRV RR, whose DNS type code is 33:

        _Service._Proto.Name TTL Class SRV Priority Weight Port Target
```

http://www.ietf.org/rfc/rfc2782.txt