compact_and_evict gets memory_to_release in bytes while
reclamation step is in segments.
Broken in f092decd90.
It doesn't make much difference with the current default step of 1
segment since we cannot reclaim less than that, so shouldn't cause
problems in practice.
Ref #4445
Message-Id: <1556013920-29676-1-git-send-email-tgrabiec@scylladb.com>
(cherry picked from commit 21fbf59fa8)