Remove suppression and implement hashCode

Original commit: elastic/x-pack-elasticsearch@0505f28e78

elasticsearch/checkstyle_suppressions.xml

@@ -5,8 +5,4 @@
 
 <suppressions>
   <!-- On Windows, Checkstyle matches files using \ path separator -->
-  <suppress files="shield[/\\]src[/\\]main[/\\]java[/\\]org[/\\]elasticsearch[/\\]shield[/\\]SystemUser.java" checks="EqualsHashCode" />
-  <suppress files="shield[/\\]src[/\\]main[/\\]java[/\\]org[/\\]elasticsearch[/\\]shield[/\\]XPackUser.java" checks="EqualsHashCode" />
-  <suppress files="watcher[/\\]src[/\\]main[/\\]java[/\\]org[/\\]elasticsearch[/\\]watcher[/\\]condition[/\\]always[/\\]ExecutableAlwaysCondition.java" checks="EqualsHashCode" />
-  <suppress files="watcher[/\\]src[/\\]main[/\\]java[/\\]org[/\\]elasticsearch[/\\]watcher[/\\]condition[/\\]never[/\\]ExecutableNeverCondition.java" checks="EqualsHashCode" />
 </suppressions>

elasticsearch/x-pack/shield/src/main/java/org/elasticsearch/shield/SystemUser.java

@@ -32,6 +32,11 @@ public class SystemUser extends User {
         return o == INSTANCE;
     }
 
+    @Override
+    public int hashCode() {
+        return System.identityHashCode(this);
+    }
+
     public static boolean is(User user) {
         return INSTANCE.equals(user);
     }

elasticsearch/x-pack/shield/src/main/java/org/elasticsearch/shield/XPackUser.java

@@ -68,6 +68,11 @@ public class XPackUser extends User {
         return INSTANCE == o;
     }
 
+    @Override
+    public int hashCode() {
+        return System.identityHashCode(this);
+    }
+
     public static boolean is(User user) {
         return INSTANCE.equals(user);
     }

elasticsearch/x-pack/watcher/src/main/java/org/elasticsearch/watcher/condition/always/ExecutableAlwaysCondition.java

@@ -35,4 +35,9 @@ public class ExecutableAlwaysCondition extends ExecutableCondition<AlwaysConditi
         return obj instanceof ExecutableAlwaysCondition;
     }
 
+    @Override
+    public int hashCode() {
+        // All instances has to produce the same hashCode because they are all equal
+        return 0;
+    }
 }

elasticsearch/x-pack/watcher/src/main/java/org/elasticsearch/watcher/condition/never/ExecutableNeverCondition.java

@@ -35,4 +35,9 @@ public class ExecutableNeverCondition extends ExecutableCondition<NeverCondition
         return obj instanceof ExecutableNeverCondition;
     }
 
+    @Override
+    public int hashCode() {
+        // All instances has to produce the same hashCode because they are all equal
+        return 0;
+    }
 }