Update databases/py-cassandra-driver to 3.4.1.

3.4.1

Bug Fixes
- Gevent connection closes on IO timeout
- "dictionary changed size during iteration" with Python 3

3.4.0

Features
- Include DSE version and workload in Host data
- Add a context manager to Cluster and Session
- Better Error Message for Unsupported Protocol Version
- Make the error message explicitly state when an error comes from
  the server
- Short Circuit meta refresh on topo change if NEW_NODE already
  exists
- Show warning when the wrong config is passed to SimpleStatement
- Return namedtuple result pairs from execute_concurrent
- BatchStatement should enforce batch size limit in a better way
- Validate min/max request thresholds for connection pool scaling
- Handle or warn about multiple hosts with the same rpc_address
- Write docs around working with datetime and timezones

Bug Fixes
- High CPU utilization when using asyncore event loop
- Fix CQL Export for non-ASCII Identifiers
- Make stress scripts Python 2.6 compatible
- UnicodeDecodeError when unicode characters in key in BOP
- WhiteListRoundRobinPolicy should resolve hosts
- Cluster and Session do not GC after leaving scope
- Don't wait for schema agreement on ignored nodes
- Reprepare on_up with many clients causes node overload
- None inserted into host map when control connection node is
  decommissioned
- weakref.ref does not accept keyword arguments


(fhajny)