Alternator allows authentication into the existing CQL roles, but
roles which have the flag "login=false" should be refused in
authentication, and this patch adds the missing check.
The patch also adds a regression test for this feature in the
test/alternator test framework, in a new test file
test/alternator/cql_rbac.py. This test file will later include more
tests of how the CQL RBAC commands (CREATE ROLE, GRANT, REVOKE)
affect authentication and authorization in Alternator.
In particular, these tests need to use not just the DynamoDB API but
also CQL, so this new test file includes the "cql" fixture that allows
us to run CQL commands, to create roles, to retrieve their secret keys,
and so on.
Fixesscylladb/scylladb#19735Closesscylladb/scylladb#19740