test: Reuse make_sstable_easy in datafile tests
test: Reuse make_sstable_easy in datafile tests

This patch is two-fold. First it changes the signature of the
local helper to facilitate next patching. Second, it makes more
relevant places in the test use this helper.

Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@scylladb.com>

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla