The current implementation of CQL type parsing worked even
when given a string representing a non-existent keyspace, as
long as the parsed type was one of the "native" types. This
implementation is going to change, so that we won't parse
types given an incorrect keyspace name.
When using `do_with_cql_env`, a "ks" keyspace is created by
default, and "tests" keyspace is not. The tests for reverse
schemas in `schema_change_test` were using the "tests"
keyspace, so in order to make the tests work after the future
changes, they now use the existing "ks" keyspace.
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