fix(event): not raise exception when begin event not found
fix(event): not raise exception when begin event not found

If begin event for database continuous event is not found, exception is raised,
that caused to db log reader crash.
Publish TestFrameworkEvent instead.

Task: https://trello.com/c/qfnjQOD5/4174-continues-events-can-cause-db-log-reader-to-crash

scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-longevity-tests,scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests,scylladb/scylla-longevity-tests