Add functionality to execute Resolver without Diagnosis.

src/main/java/com/microsoft/dhalion/api/IHealthPolicy.java

@@ -68,6 +68,15 @@ public interface IHealthPolicy {
    */
   Collection<Action> executeResolvers(Collection<Diagnosis> diagnosis);
 
+  /**
+   * Invoked in the event that the policy should be overridden, this method executes one {@link IResolver} to fix a
+   * single identified issue.
+   *
+   * @param resolver a resolver to be executed
+   * @return actions executed to mitigate health issues
+   */
+  Collection<Action> executeResolver(IResolver resolver);
+
   /**
    * @return the remaining delay before re-execution of this policy
    */

src/main/java/com/microsoft/dhalion/api/IResolver.java

@@ -34,6 +34,15 @@ default Collection<String> getActionTypes() {
   default void initialize(ExecutionContext context) {
   }
 
+  /**
+   * Triggers execution of {@link Action}s which are expected to improved system health.
+   *
+   * @return all the actions executed by this resolver
+   */
+  default Collection<Action> resolve() {
+    throw new UnsupportedOperationException();
+  }
+
   /**
    * Triggers execution of {@link Action}s which are expected to improved system health.
    *

src/main/java/com/microsoft/dhalion/events/EventDispatcher.java

@@ -15,7 +15,7 @@ public class EventDispatcher<T> implements EventHandler<T> {
 
   public synchronized void addHandler(EventHandler<T> handler) {
     if (handlers.contains(handler)) {
-      throw new IllegalArgumentException("Duplicate hanlder registration");
+      throw new IllegalArgumentException("Duplicate handler registration");
     }
     handlers.add(handler);
   }

src/main/java/com/microsoft/dhalion/policy/HealthPolicyImpl.java

@@ -165,6 +165,24 @@ public Collection<Action> executeResolvers(Collection<Diagnosis> diagnosis) {
     return actions;
   }
 
+  @Override
+  public Collection<Action> executeResolver(IResolver resolver) {
+    if (oneTimeDelay != null && !oneTimeDelay.isAfter(clock.now())) {
+      // reset one time delay timestamp
+      oneTimeDelay = null;
+    }
+
+    Collection<Action> actions = new ArrayList<>();
+    if (!resolvers.contains(resolver)) {
+      return actions;
+    }
+
+    actions = resolver.resolve();
+
+    lastExecutionTimestamp = clock.now();
+    return actions;
+  }
+
   @Override
   public Duration getDelay() {
     long delay;