When reading tablet replicas from system.tablets, we need to refer to
the base table partition, if any.
We fix and simplify the test api for reading tablet replicas to read
from the base table.
ALTERing tablets-enabled KEYSPACES (KS) didn't account for materialized
views (MV), and only produced tablets mutations changing tables.
With this patch we're producing tablets mutations for both tables and
MVs, hence when e.g. we change the replication factor (RF) of a KS, both the
tables' RFs and MVs' RFs are updated along with tablets replicas.
The `test_tablet_rf_change` testcase has been extended to also verify
that MVs' tablets replicas are updated when RF changes.
Fixes: #20240Closesscylladb/scylladb#21007
Replaced the old `read_barrier` helper from "test/pylib/util.py"
by the new helper from "test/pylib/rest_client.py" that is calling
the newly introduced direct REST API.
Replaced in all relevant tests and decommissioned the old helper.
Introduced a new helper `get_host_api_address` to retrieve the host API
address - which in come cases can be different from the host address
(e.g. if the RPC address is changed).
Fixes: scylladb/scylladb#19662Closesscylladb/scylladb#19739
