test: Set test change estimation to 1
test: Set test change estimation to 1

The test intention is not to test how zero estimated partitions
work, there's another case for than (in another test). Also it
looks like 0 is doesn't flow anywhere far, it's std::max-ed into
1 early inside mc::writer constructor.

This changes significantly simplifies the unification of the set
of make_sstable_easy()-s in the next patch.

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

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