Tests for CASSANDRA-6430
Cover non-EXISTS conditions, too
Import since in thrift_tests.py
Set rpc_max_threads=20 for thrift_hsha_test test_6285
Update thrift_tests.py

get_multi_slice() is added on 2.1, which is not found on 2.0.10
Merge pull request #99 from AlfredChenxf/patch-2

Update thrift_tests.py
Merge branch 'master' into ccm_develop