adding test files and starting to rework the pool
making ConnectionPool not use a global state
setup now creates a global connection pool
fixing references to removed vars
Getting connection pooling working with mocking library

Verified throwing exception when no servers are available,
but correctly recovering and hitting the next server when
one is.

fixing minor pooling tests

ensure we get the right exception back when no servers are available

working on tests for retry

connections working despite failure

Removed old connection_manager and replaced with a simple context
manager that allows for easy access to clients within the main pool
test comment
Merge pull request #56 from bdeggleston/improved_connections

Improved connection pooling