Improve shardsCleanup test

When startNode exits there is no guarantee that shard cleanup is finished because the cleanup operation is performed on another thread and startNode doesn't wait for it to complete. Therefore we might need to wait for the shard to disappear.
Make facet and sort tests more reliable in case of multiple nodes and shards

Stats, histogram and range facets and sorting currently fail if a field that they are running on is not defined in the mapping. In case of dynamic fields it might mean that by the time the facet query is executed the new field mapping might not be propagated to all nodes yet.
Allow health to be executed on a local node instead of the master
Improve SearchStatsTests

Added refresh to guarantee that at least something will be fetched on a fast computer.