dist/common/scripts/scylla_setup: fix gentoo linux installed package detection
dist/common/scripts/scylla_setup: fix gentoo linux installed package detection

return code is expected to be 0 when installed package was found

Signed-off-by: Alexys Jacob <ee25f2b26a23c85eb2940a5214ecb1801c877d19@gentoo.org>
Message-Id: <20181002123433.4702-1-ee25f2b26a23c85eb2940a5214ecb1801c877d19@gentoo.org>

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