allocations may enter the gate, so it would be wise for us to wait for them.
Fixes #1860
Signed-off-by: Glauber Costa <glauber@scylladb.com>
Message-Id: <53cd6996c1cbd8b38bab3b03604bd11e5c20beda.1479650012.git.glauber@scylladb.com>
(cherry picked from commit 21c1e2b48c)