[Tests] Disabling testAckedIndexing

The test is currently unstable and needs some more work
Fixed compilation issue caused by the lack of a thread pool name
[TEST] Added test to verify if 'discovery.zen.rejoin_on_master_gone' is updatable at runtime.
[TEST] Verify no master block during partition for read and write apis
[TEST] Make sure get request is always local
Added java docs to all tests in DiscoveryWithNetworkFailuresTests

Moved testVerifyApiBlocksDuringPartition to test blocks rather then rely on specific API rejections.
Did some cleaning while at it.
[Tests] improved automatic disruption healing after tests
[TEST] Properly clear the disruption schemes after test completed.
[Test] testVerifyApiBlocksDuringPartition - wait for stable cluster after partition
[Discovery] immediately start Master|Node fault detection pinging

After a node joins the clusters, it starts pinging the master to verify it's health. Before, the cluster join request was processed async and we had to give some time to complete. With  #6480 we changed this to wait for the join process to complete on the master. We can therefore start pinging immediately for fast detection of failures. Similar change can be made to the Node fault detection from the master side.

Closes #6706
[Discovery] Start master fault detection after pingInterval

This is to allow the master election to complete on the chosen master.

 Relates to #6706
[Tests] Use local gateway

This is important to for proper primary allocation decisions
[Tests] Don't log about restoring a partition if the partition is not active.
[Tests] Increase timeout when waiting for partitions to heal

the current 30s addition is tricky because we use 30s as timeout in many places...
[Internal] Migrate new initial state cluster update task to a ClusterStateNonMasterUpdateTask
[logging] don't log an error if scheduled reroute is rejected because local node is no longer master

Since it runs in a background thread after a node is added, or submits a cluster state update when a node leaves, it may be that by the time it is executed the local node is no longer master.
Remove unneeded reference to DiscoveryService which potentially causes circular references
[Tests] Introduced ClusterDiscoveryConfiguration

Closes #6890
[Tests] stability improvements

added explicit cleaning of temp unicast ping results
reduce gateway local.list_timeout to 10s.
testVerifyApiBlocksDuringPartition: verify master node has stepped down before restoring partition
[Store] migrate non-allocated shard deletion to use ClusterStateNonMasterUpdateTask