add pre-shutdown action to be executed inside ChronicleHashCloseOnExitHook.

This is useful when we want to do an orderly shutdown.
For example: To carry out graceful shutdown and explicitly control when a ChronicleHash
is closed, a pre-shutdown action can be a wait on a CountDownLatch that would be released
appropriately.

src/main/java/net/openhft/chronicle/map/ChronicleMapBuilder.java

@@ -181,6 +181,7 @@ public final class ChronicleMapBuilder<K, V> implements
     MapMethods<K, V, ?> methods = DefaultSpi.mapMethods();
     MapEntryOperations<K, V, ?> entryOperations = mapEntryOperations();
     MapRemoteOperations<K, V, ?> remoteOperations = mapRemoteOperations();
+    Runnable preShutdownAction;
     private String name;
     // not final because of cloning
     private ChronicleMapBuilderPrivateAPI<K, V> privateAPI =
@@ -1587,6 +1588,11 @@ public final class ChronicleMapBuilder<K, V> implements
                 corruptionListener);
     }
 
+    @Override
+    public void setPreShutdownAction(Runnable preShutdownAction) {
+        this.preShutdownAction = preShutdownAction;
+    }
+
     @Override
     public ChronicleMap<K, V> create() {
         // clone() to make this builder instance thread-safe, because createWithoutFile() method