Use CL.ONE explicitly when interacting with the system keyspace

The system keyspace uses  "LocalStrategy" for replication so it needs to
be accessed with CL.ONE. If the default consistency level is set to
something else all management commands which rely on introspecting the
system keyspace will fail.
Make get_table_settings use CL.ONE explicitly
Merge branch 'system-keyspace-cl-one' of https://github.com/dokai/cqlengine into system-keyspace-cl-one