Revert "Improve handling of failed primary replica handling"

This reverts commit 75ed24f6b6a96ac268f7b085550020252d94d908.
[Test] testCorruptionOnNetworkLayer had a typo in test name.
[TEST] Temporarily don't corrupt .del files since they are generational and we might pick the wrong one
[TEST] Fix CorruptedFileTest to always corrupt the latest delete generation if a .del file is picked
Improve handling of failed primary replica handling
Out of #6808, we improved the handling of a primary failing to make sure replicas that are initializing are properly failed as well. After double checking it, it has 2 problems, the first, if the same shard routing is failed again, there is no protection that we don't apply the failure (which we do in failed shard cases), and the other was that we already tried to handle it (wrongly) in the elect primary method.
This change fixes the handling to work correctly in the elect primary method, and adds unit tests to verify the behavior
The change also expose a problem in our handling of replica shards that stay initializing during primary failure and electing another replica shard as primary, where we need to cancel its ongoing recovery to make sure it re-starts from the new elected primary
closes #6825
More Like This: ensures selection of best terms is indeed O(n)

Previously the size of the priority queue was wrongly set to the total number
of terms. Instead, it should be set to 'maxQueryTerms'. This makes the
selection of best terms O(n), instead of O(n*log(n)).

Jira patch: https://issues.apache.org/jira/browse/LUCENE-5795

Closes #6657
[Gateway] set a default of 5m to `recover_after_time` when any to the `expected*Nodes` is set

The `recovery_after_time` tells the gateway to wait before starting recovery from disk. The goal here is to allow for more nodes to join the cluster and thus not start potentially unneeded replications. The `expectedNodes` setting (and friends) tells the gateway when it can start recovering even if the `recover_after_time` has not yet elapsed. However, `expectedNodes` is useless if one doesn't set `recovery_after_time`. This commit changes that by setting a sensible default of 5m for `recover_after_time` *if* a `expectedNodes` setting is present.

Closes #6742
Only use IndexShard instance to lookup recovery status
make sure we use the instance itself to look it up, and not the shard id, as we might get another instance
leftover from #6825
Docs: fix merge docs to match the code (the max_thread_count default is 'aggressive' (favor SSDs))
Throw exception if function in function score query is null

closes #6292 #6784
Docs: remove orphan comma
[Tests] Enhance ZenUnicastDiscoveryTest

This started out as a simple correction to a missing setting problem, but go bigger into more general work on the ZenUnicastDiscoveryTets suite. It now works with both network and local mode. I also merge the different ZenUnicast test suites into a single place.

Closes #6835
Cleanup of the transport request/response messages

Now both TransportRequest and TransportResponse inherit from a base TransportMessage that holds the message headers and also now added the remote transport address (where this message came from).
Print trace log if not enough master nodes could be found.
[TEST] Ensure that one node is part of the cluster.
Docs: Fixed invalid word count in geodistance agg doc

Closes #6838
[Test] testHostOnMessages - only decrease latch after setting transport addresses
[TEST] wait for green before deleting mapping
[TEST] wait for green before deleting mapping
Snapshot/Restore: Add ability to restore indices without their aliases

Closes #6457