Fix sync_test_full

[kevin-harrison]

Enabling Unicache can result in a flawed prepare phase.

---- sync_full_test stdout ----

thread 'sync_full_test' panicked at omnipaxos/tests/sync_test.rs:266:13:
Error on collecting futures of decided proposals: The timeout expired..
Follower log: [Snapshotted(SnapshottedEntry { trimmed_idx: 5, snapshot: ValueSnapshot { latest_value: Value { id: 5, first_name: "5", last_name: "5", job: "5" }, snapshotted: [Value { id: 1, first_name: "1", last_name: "1", job: "1" }, Value { id: 2, first_name: "2", last_name: "2", job: "2" }, Value { id: 3, first_name: "3", last_name: "3", job: "3" }, Value { id: 6, first_name: "6", last_name: "6", job: "6" }, Value { id: 7, first_name: "7", last_name: "7", job: "7" }, Value { id: 4, first_name: "4", last_name: "4", job: "4" }, Value { id: 5, first_name: "5", last_name: "5", job: "5" }] }, _p: PhantomData<sync_test::utils::Value> })]
 Leader log: [Snapshotted(SnapshottedEntry { trimmed_idx: 2, snapshot: ValueSnapshot { latest_value: Value { id: 2, first_name: "2", last_name: "2", job: "2" }, snapshotted: [Value { id: 1, first_name: "1", last_name: "1", job: "1" }, Value { id: 2, first_name: "2", last_name: "2", job: "2" }] }, _p: PhantomData<sync_test::utils::Value> }), Decided(Value { id: 3, first_name: "3", last_name: "3", job: "3" }), Decided(Value { id: 4, first_name: "4", last_name: "4", job: "4" }), Decided(Value { id: 5, first_name: "5", last_name: "5", job: "5" }), Decided(Value { id: 10, first_name: "10", last_name: "10", job: "10" }), Decided(Value { id: 11, first_name: "11", last_name: "11", job: "11" }), Decided(Value { id: 12, first_name: "12", last_name: "12", job: "12" }), StopSign(StopSign { next_config: ClusterConfig { configuration_id: 2, nodes: [1, 2, 3], flexible_quorum: None }, metadata: None }, true)]
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace


failures:
    sync_full_test