dist: scylla_lib.sh: get_mode_cpu_set: don't let the error messages out
dist: scylla_lib.sh: get_mode_cpu_set: don't let the error messages out

References #3508

Signed-off-by: Vlad Zolotarov <976c0f8d0852ed6439ad273880b400a75a7c41d0@scylladb.com>
Message-Id: <1529702903-24909-2-git-send-email-976c0f8d0852ed6439ad273880b400a75a7c41d0@scylladb.com>

avikivity/scylla,scylladb/scylla,duarten/scylla,scylladb/scylla,scylladb/scylla,duarten/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla,duarten/scylla