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 RFC seems like a sane default. This will certainly cause us pain on the next release. We might want to hold off on merging this unless someone else complains until we have a own our packaging to change the defaults.