sstable tests: test set_generation
sstable tests: test set_generation

No code works until it's been tested.

Signed-off-by: Glauber Costa <f8b79557d19b40666ebe336545a0b6178af65685@scylladb.com>

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