Watcher: use same value of watcher state (elastic/x-pack-elasticsearch#4430)

This commit updates the WatcherLifecycleService to use the same value
for the watcher service state when making comparisons to determine the
actions that need to be taken.

See elastic/x-pack-elasticsearch#4429

Original commit: elastic/x-pack-elasticsearch@c6c24fc

Author: jaymode

plugin/watcher/src/main/java/org/elasticsearch/xpack/watcher/WatcherLifeCycleService.java

@@ -87,7 +87,7 @@ private synchronized void start(ClusterState state) {
         if (shutDown) {
             return;
         }
-        WatcherState watcherState = watcherService.state();
+        final WatcherState watcherState = watcherService.state();
         if (watcherState != WatcherState.STOPPED) {
             logger.debug("not starting watcher. watcher can only start if its current state is [{}], but its current state now is [{}]",
                     WatcherState.STOPPED, watcherState);
@@ -162,9 +162,10 @@ public void clusterChanged(ClusterChangedEvent event) {
             clearAllocationIds();
             executor.execute(() -> this.stop("watcher manually marked to shutdown by cluster state update"));
         } else {
-            if (watcherService.state() == WatcherState.STARTED && event.state().nodes().getLocalNode().isDataNode()) {
+            final WatcherState watcherState = watcherService.state();
+            if (watcherState == WatcherState.STARTED && event.state().nodes().getLocalNode().isDataNode()) {
                 checkAndSetAllocationIds(event.state(), true);
-            } else if (watcherService.state() != WatcherState.STARTED && watcherService.state() != WatcherState.STARTING) {
+            } else if (watcherState != WatcherState.STARTED && watcherState != WatcherState.STARTING) {
                 IndexMetaData watcherIndexMetaData = WatchStoreUtils.getConcreteIndex(Watch.INDEX, event.state().metaData());
                 IndexMetaData triggeredWatchesIndexMetaData = WatchStoreUtils.getConcreteIndex(TriggeredWatchStoreField.INDEX_NAME,
                         event.state().metaData());