Log Message:
Update databases/py-cassandra-driver to 3.6.0.

Features
- Handle null values in NumpyProtocolHandler (PYTHON-553)
- Collect greplin scales stats per cluster (PYTHON-561)
- Update mock unit test dependency requirement (PYTHON-591)
- Handle Missing CompositeType metadata following C* upgrade
  (PYTHON-562)
- Improve Host.is_up state for HostDistance.IGNORED hosts
  (PYTHON-551)
- Utilize v2 protocol's ability to skip result set metadata for
  prepared statement execution (PYTHON-71)
- Return from Cluster.connect() when first contact point
  connection(pool) is opened (PYTHON-105)
- cqlengine: Add ContextQuery to allow cqlengine models to switch
  the keyspace context easily (PYTHON-598)
- Standardize Validation between Ascii and Text types in Cqlengine
  (PYTHON-609)

Bug Fixes
- Fix geventreactor with SSL support (PYTHON-600)
- Don't downgrade protocol version if explicitly set (PYTHON-537)
- Nonexistent contact point tries to connect indefinitely
  (PYTHON-549)
- Execute_concurrent can exceed max recursion depth in failure
  mode (PYTHON-585)
- Libev loop shutdown race (PYTHON-578)
- Include aliases in DCT type string (PYTHON-579)
- cqlengine: Comparison operators for Columns (PYTHON-595)
- cqlengine: disentangle default_time_to_live table option from
  model query default TTL (PYTHON-538)
- cqlengine: pk__token column name issue with the equality
  operator (PYTHON-584)
- cqlengine: Fix "__in" filtering operator converts True to string
  "True" automatically (PYTHON-596)
- cqlengine: Avoid LWTExceptions when updating columns that are
  part of the condition (PYTHON-580)
- cqlengine: Cannot execute a query when the filter contains all
  columns (PYTHON-599)
- cqlengine: routing key computation issue when a primary key
  column is overriden by model inheritance (PYTHON-576)