sdcm/fill_db_data: fix expect result bype of empty blob (#1499)
sdcm/fill_db_data: fix expect result bype of empty blob (#1499)

In Python3 the driver returns blob as byte object.

Signed-off-by: Amos Kong <eb01d8f828a6c9a20be4534e72e049aaf41503df@scylladb.com>
scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-longevity-tests