In test_cdc_generation_clearing we trigger events that update CDC
generations, verify the generations are updated as expected, and verify
the system topology and CDC generations are consistent on all nodes.
Before checking that all nodes are consistent and have the same CDC
generations, we need to consider that the changes are propagated through
raft and take some time to propagate to all nodes.
Currently, we wait for the change to be applied only on the first server
which runs the CDC generation publisher fiber and read the CDC
generations from this single node. The consistency check that follows
could fail if the change was not propagated to some other node yet.
To fix that, before checking consistency with all nodes, we execute a
read barrier on all nodes so they all see the same state as the leader.
Fixesscylladb/scylladb#24407Closesscylladb/scylladb#24433
Rework `ScyllaLogFile.wait_for()` method to make it easier
to add required methods to ScyllaNode class of ccm-like shim.
Also, added `ScyllaLogFile.grep_for_errors()` method and
reworked `ScyllaLogFile.grep()`
