clusterAggregate does not handle the case when aggregate fails due to SSV or snapshot errors

This invariant will fail
The try catch block https://github.com/mongodb/mongo/blob/r3.7.5/src/mongo/s/commands/cluster_aggregate.cpp#L455-L509 does not handle the case that it will exhaust the attempts so it returns empty results.

When its fixed the cluster_aggregate_test needs to get updated as well to include a currently disabled test.