Failed search on a shard tries a local replica on a network thread
When a search on a shard to a remove node fails, and then replica exists on the local node, then the execution of the search is done on the network thread. This is problematic since we need to execute it on the actual search thread pool, but can also explain #4519, where the get happens on the network thread and it waits to send the get request till the network thread we use is freed (deadlock...)
fixes #4526

note, re-enable the geo shape fetch test, this fix should solve it as well