Use whether react instance is accepting calls to determine whether instance is active

Summary:
There was previously a race condition where hasActiveCatalystInstance would return true, but calling a JS module call on it would result in a crash. Now, hasActivtyCatalystInstance will only return true once the instance is actually accepting calls.

I'll follow this up with a more risky diff that gets rid of hasActiveCatalystInstance and just queues JS calls until runJSBundle is called.

Reviewed By: javache

Differential Revision: D4117374

fbshipit-source-id: 60941f68b0906a8213571305c564bfe3d053f51b

ReactAndroid/src/main/java/com/facebook/react/bridge/CatalystInstance.java

@@ -40,6 +40,7 @@ public interface CatalystInstance extends MemoryPressureListener {
    */
   void destroy();
   boolean isDestroyed();
+  boolean isAcceptingCalls();
 
   /**
    * Initialize all the native modules