[RUBY-41] prevent connections to ignored hosts

* Ensure the driver never attempts to connect to hosts in
  remote datacenters when remove dcs must be ignored
* Reverse the order of notifications on host_down/host_lost
  events to have load balancing policy updated before
  control connection
* Check load balancing distance when starting to
  continuously reconnect to down hosts
[ci skip] update CHANGELOG
fix automatic reconnection scenario
move scenarios with multiple datacenters to the end
skip ignored hosts when connecting
retrieve distance once when connecting session
Merge pull request #29 from datastax/RUBY-41

[RUBY-41] prevent connections to ignored hosts