Revert "fix(run_user_stress_in_batches): start nemesis thread after stress"
Revert "fix(run_user_stress_in_batches): start nemesis thread after stress"

This reverts commit 2a918d38b9537a907595cbebb2f236a14b22a834.

This commit broke running in batches of the test_user_batch_custom_time.

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