Move configuration functions to rt_config.

- functions include set_conf/2, set_advanced_conf/2, and
  update_app_config/2.
Continue to move config functions from rt to rt_config.
Migrate several more functions into rt_cluster from rt.
Move backend related functions from rt module to new rt_backend module.
Move protobuf-related functions from rt module to rt_pb.
Fix rt_pb function exports.
Refactor http-relate rt functions

- Move rt module functions to new rt_http module.
- Convert http_bucket_types to new test convention.
Move node-related functions from rt module to rt_node.
Move rt:brutal_kill to rt_node.
Move ring-related rt functions to rt_ring; some cleanup.
Move command-line oriented rt functions to rt_cmd_line.
Move bucket types related functions from rt module to rt_bucket_types.
Move AAE related functions from rt module to rt_aae.
More functions moved to rt_node.
Move rt:is_pingable to rt_node.
Move systest read/write functions from rt module to rt_systest.
Fix calls to rt:teardown; should be rt_cluster:teardown.
Merge pull request #669 from basho/feature/jra/decouple-rt-refactor

Refactor and break up rt module into appropriate subdomain functions