We limit the number of concurrent blob downloads per node and per recovery, but if a user configures too many concurrent recoveries they may run out of per-node download permits which yields the following message:

> Unable to acquire permit to use snapshot files during recovery, this recovery will recover index files from the source node. Ensure snapshot files can be used during recovery by setting [indices.recovery.max_concurrent_snapshot_file_downloads] to be no greater than [25]

The `[25]` here is wrong, the 25 permits are shared across all inbound recoveries so we should divide the suggested value by `cluster.routing.allocation.node_concurrent_incoming_recoveries`. In extreme cases the user may have configured so many concurrent recoveries that the only reasonable limit is zero, and in that case we should suggest setting `indices.recovery.use_snapshots: false` instead.


test/framework/src/main/java/org/elasticsearch/test/MockLogAppender.java
public SeenEventExpectation(String name, String logger, Level level, String message) {
            super(name, logger, level, message);
        }
        @Override
        public void assertMatched() {
            assertThat("expected to see " + name + " but did not", saw, equalTo(true));
        }
    }
    public static class EventuallySeenEventExpectation extends SeenEventExpectation {
        private volatile boolean expectSeen = false;
        public EventuallySeenEventExpectation(String name, String logger, Level level, String message) {
            super(name, logger, level, message);
        }
        public void setExpectSeen() {
            expectSeen = true;
        }
        @Override
        public void assertMatched() {
            if (expectSeen) {
                super.assertMatched();
            } else {
                assertThat("expected not to see " + name + " yet but did", saw, equalTo(false));
            }
        }
    }
    public static class ExceptionSeenEventExpectation extends SeenEventExpectation {