Upon being elected as master, prefer joins' node info to existing cluster state (#19743)

When we introduces [persistent node ids](https://github.com/elastic/elasticsearch/pull/19140) we were concerned that people may copy data folders from one to another resulting in two nodes competing for the same id in the cluster. To solve this we elected to not allow an incoming join if a different with same id already exists in the cluster, or if some other node already has the same transport address as the incoming join. The rationeel there was that it is better to prefer existing nodes and that we can rely on node fault detection to remove any node from the cluster that isn't correct any more, making room for the node that wants to join (and will keep trying).

Sadly there were two problems with this:
1) One minor and easy to fix - we didn't allow for the case where the existing node can have the same network address as the incoming one, but have a different ephemeral id (after node restart). This confused the logic in `AllocationService`, in this rare cases. The cluster is good enough to detect this and recover later on, but it's not clean.
2) The assumption that Node Fault Detection will clean up is *wrong* when the node just won an election (it wasn't master before) and needs to process the incoming joins in order to commit the cluster state and assume it's mastership. In those cases, the Node Fault Detection isn't active. 

This PR fixes these two and prefers incoming nodes to existing node when finishing an election. 
On top of the, on request by @ywelsch , `AllocationService` synchronization between the nodes of the cluster and it's routing table is now explicit rather than something we do all the time. The same goes for promotion of replicas to primaries.

1 files changed, 1 insertions, 1 deletions

diff --git a/core/src/test/java/org/elasticsearch/action/ingest/IngestProxyActionFilterTests.java b/core/src/test/java/org/elasticsearch/action/ingest/IngestProxyActionFilterTests.java
index 3d1a1a1c69..a602465197 100644
--- a/core/src/test/java/org/elasticsearch/action/ingest/IngestProxyActionFilterTests.java
+++ b/core/src/test/java/org/elasticsearch/action/ingest/IngestProxyActionFilterTests.java
@@ -79,7 +79,7 @@ public class IngestProxyActionFilterTests extends ESTestCase {
                 roles.add(DiscoveryNode.Role.INGEST);
             }
             DiscoveryNode node = new DiscoveryNode(nodeId, nodeId, LocalTransportAddress.buildUnique(), attributes, roles, VersionUtils.randomVersion(random()));
-            builder.put(node);
+            builder.add(node);
             if (i == totalNodes - 1) {
                 localNode = node;
             }