tests/gossip_test: Use RAII for orderly destruction
tests/gossip_test: Use RAII for orderly destruction

Change the test so that services are correctly teared down, by the
correct order (e.g., storage_service access the messaging_service when
stopping).

Signed-off-by: Duarte Nunes <a60e8b7496f7715d71354fe4c06dd24017025bf1@scylladb.com>
Message-Id: <20180814112111.8521-2-a60e8b7496f7715d71354fe4c06dd24017025bf1@scylladb.com>

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