Fix AutoFollowCoordinatorTests#testExcludedPatternIndicesAreNotAutoFollowed

Use an empty ClusterState as a base cluster state to take into account
the case where no leader candidate indices are created

Closes elastic#73797
Relates elastic#72935
Backport of elastic#73811

Author: fcofdez

x-pack/plugin/ccr/src/test/java/org/elasticsearch/xpack/ccr/action/AutoFollowCoordinatorTests.java

@@ -2089,15 +2089,11 @@ public void testExcludedPatternIndicesAreNotAutoFollowed() {
                         Collections.singletonMap(pattern, emptyMap()))))
             .build();
 
-        ClusterState remoteState = null;
+        ClusterState remoteState = ClusterState.EMPTY_STATE;
         final int nbLeaderIndices = randomIntBetween(0, 15);
         for (int i = 0; i < nbLeaderIndices; i++) {
             String indexName = "docs-" + i;
-            if (remoteState == null) {
-                remoteState = createRemoteClusterState(indexName, true);
-            } else {
-                remoteState = createRemoteClusterState(remoteState, indexName);
-            }
+            remoteState = createRemoteClusterState(remoteState, indexName);
         }
 
         final int nbLeaderExcludedIndices = randomIntBetween(1, 15);