Use `Node`'s connection pool when (re)configuring node
saves lots of connection accept/close cycles
Bugfix in accessing `connection._pool`
use --smallfiles to start mongo servers
Travic CI support
Database._initialized nerver can be False
  It may be present or not, but if present, it's True
Apply PEP8
Don't call `_config_nodes` when another `_config_nodes` is in progress
If we call `get_node` twice before starting IOLoop, `_config_nodes` will be called twice, and therefore subsequent `_config_nodes` will be called twice every 30-seconds.