CLI tool: Fix exit status changes

In elastic/elasticsearch#12165 the return value of the CLITool was changed from an integer
to the ExitStatus enum. This commit adapts the cli tools of x-plugins.

Original commit: elastic/x-pack-elasticsearch@fc6478bfa5

shield/src/main/java/org/elasticsearch/shield/authc/esusers/tool/ESUsersTool.java

@@ -42,8 +42,8 @@ public class ESUsersTool extends CliTool {
             .build();
 
     public static void main(String[] args) {
-        int status = new ESUsersTool().execute(args);
-        System.exit(status);
+        ExitStatus exitStatus = new ESUsersTool().execute(args);
+        System.exit(exitStatus.status());
     }
 
     public ESUsersTool() {

shield/src/main/java/org/elasticsearch/shield/crypto/tool/SystemKeyTool.java

@@ -36,8 +36,8 @@ public class SystemKeyTool extends CliTool {
 
 
     public static void main(String[] args) throws Exception {
-        int status = new SystemKeyTool().execute(args);
-        System.exit(status);
+        ExitStatus exitStatus = new SystemKeyTool().execute(args);
+        System.exit(exitStatus.status());
     }
 
     private static final CliToolConfig CONFIG = config("syskey", SystemKeyTool.class)

watcher/src/main/java/org/elasticsearch/watcher/trigger/schedule/tool/CronEvalTool.java

@@ -31,8 +31,8 @@ public class CronEvalTool extends CliTool {
             .build();
 
     public static void main(String[] args) throws Exception {
-        int status = new CronEvalTool().execute(args);
-        System.exit(status);
+        ExitStatus exitStatus = new CronEvalTool().execute(args);
+        System.exit(exitStatus.status());
     }
 
     public CronEvalTool() {