CASSANDRA-6313

https://issues.apache.org/jira/browse/CASSANDRA-6313
http://cassci.datastax.com/job/cassandra-2.1_dtest_pydriver/

Use the DataStax python driver instead of dbapi2. Using the new python driver allows us to test over the native binary protocol rather than using cql over thrift. 
Given that we will likely be merging sometime soon as 2.1.0 is on rc7, I am opening this PR now so that we can review it thoroughly before merging.