[TEST] Provide overloaded indexRandom to opt out of dummy documents
[TEST] Opt out of dummy documents where scores are relevant.
Honor time delay when retrying recoveries

In some places we want to delay the start of a shard recovery because the source node is not ready to receive. At the moment the retry logic ignores the time delay parameter (`retryAfter`) causing a busy waiting like scenario. This is fixed in this commit.

Closes #6226
Before deleting a local unused shard copy, verify we're connected to the node it's supposed to be on

This is yet another safety guard to make sure we don't delete data if the local copy is the only one (even if it's not part of the cluster state any more)

Closes #6191