tests: add test for sstable set's incremental selector
tests: add test for sstable set's incremental selector

Signed-off-by: Raphael S. Carvalho <1e2942cea40e3b4d2162dfcd9e53e41c05a84d22@scylladb.com>

raphaelsc/scylla,scylladb/scylla,duarten/scylla,duarten/scylla,duarten/scylla,avikivity/scylla,raphaelsc/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla,avikivity/scylla,raphaelsc/scylla,scylladb/scylla