Move replication tests to separate subdirectory
Move rebar plugin to separate directory
Add missing node function to rt.erl
Remove direct calls to rtdev harness from replication tests
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.