Improve version checking in test util includes

In addition to adding version checking for the shard cluster, I fixed the following bugs (quoted from the commit message):

> mongos.inc was comparing the server version and $needs version backwards. Additionally, it was only checking the standalone server version.
> 
> replicaset.inc and standalone.inc were defaulting to ">", instead of ">=".
> 
> unix-standalone.inc was ignoring $needsOp and always performing a "<" comparison.