[Test] Wait for clsuter to form before assertions (elastic#130973)

The original cluster should be properly formed before the tests kick
off. This PR ensures that.

Relates: elastic#129118 Resolves: elastic#130883 Resolves: elastic#130979

Author: ywangd

muted-tests.yml

@@ -564,15 +564,9 @@ tests:
 - class: org.elasticsearch.cluster.ClusterStateSerializationTests
   method: testSerializationPreMultiProject
   issue: https://github.com/elastic/elasticsearch/issues/130872
-- class: org.elasticsearch.cluster.coordination.votingonly.VotingOnlyNodePluginTests
-  method: testPreferFullMasterOverVotingOnlyNodes
-  issue: https://github.com/elastic/elasticsearch/issues/130883
 - class: org.elasticsearch.search.SearchWithRejectionsIT
   method: testOpenContextsAfterRejections
   issue: https://github.com/elastic/elasticsearch/issues/130821
-- class: org.elasticsearch.cluster.coordination.votingonly.VotingOnlyNodePluginTests
-  method: testVotingOnlyNodesCannotBeMasterWithoutFullMasterNodes
-  issue: https://github.com/elastic/elasticsearch/issues/130979
 - class: org.elasticsearch.packaging.test.DockerTests
   method: test082CannotUseEnvVarsAndFiles
   issue: https://github.com/elastic/elasticsearch/issues/129808

x-pack/plugin/voting-only-node/src/internalClusterTest/java/org/elasticsearch/cluster/coordination/votingonly/VotingOnlyNodePluginTests.java

@@ -96,12 +96,12 @@ public void testPreferFullMasterOverVotingOnlyNodes() throws Exception {
         internalCluster().setBootstrapMasterNodeIndex(0);
         internalCluster().startNodes(2);
         internalCluster().startNode(addRoles(Set.of(DiscoveryNodeRole.VOTING_ONLY_NODE_ROLE)));
-        internalCluster().startDataOnlyNodes(randomInt(2));
-        assertBusy(
-            () -> assertThat(
-                clusterAdmin().prepareState(TEST_REQUEST_TIMEOUT).get().getState().getLastCommittedConfiguration().getNodeIds().size(),
-                equalTo(3)
-            )
+        final int numDataNodes = randomInt(2);
+        internalCluster().startDataOnlyNodes(numDataNodes);
+        internalCluster().validateClusterFormed();
+
+        awaitClusterState(
+            state -> state.getLastCommittedConfiguration().getNodeIds().size() == 3 && state.nodes().size() == 3 + numDataNodes
         );
         final String originalMaster = internalCluster().getMasterName();
 
@@ -157,15 +157,14 @@ public void testVotingOnlyNodesCannotBeMasterWithoutFullMasterNodes() throws Exc
         internalCluster().setBootstrapMasterNodeIndex(0);
         internalCluster().startNode();
         internalCluster().startNodes(2, addRoles(Set.of(DiscoveryNodeRole.VOTING_ONLY_NODE_ROLE)));
-        internalCluster().startDataOnlyNodes(randomInt(2));
-        assertBusy(
-            () -> assertThat(
-                clusterAdmin().prepareState(TEST_REQUEST_TIMEOUT).get().getState().getLastCommittedConfiguration().getNodeIds().size(),
-                equalTo(3)
-            )
+        final int numDataNodes = randomInt(2);
+        internalCluster().startDataOnlyNodes(numDataNodes);
+        internalCluster().validateClusterFormed();
+
+        awaitClusterState(
+            state -> state.getLastCommittedConfiguration().getNodeIds().size() == 3 && state.nodes().size() == 3 + numDataNodes
         );
-        awaitMasterNode();
-        final String oldMasterId = clusterAdmin().prepareState(TEST_REQUEST_TIMEOUT).get().getState().nodes().getMasterNodeId();
+        final String oldMasterId = internalCluster().getMasterName();
 
         internalCluster().stopCurrentMasterNode();
         awaitMasterNotFound();