This updates all service discoveries to correctly build the __address__ label for IPv6 addresses.
This commit changes the TargetProvider interface to use a context.Context and send lists of TargetGroups, rather than single ones.
nerve's registration format differs from serverset. With this commit there is now a dedicated treecache file in util, and two separate files for serverset and nerve. Reference: https://github.com/airbnb/nerve
Fabian Reinartz
Tobias Schmidt
Julien Dehee