fix(tester.py): reorganize code
fix(tester.py): reorganize code

cl_params addes 2 params to common_params, for mixed_scylla we rewrite two of them.
it is better to pick common_params and add missing parameter to it

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