Fixing race condition in creating and subscribing application in api-manager side

components/apimgt-extensions/org.wso2.carbon.apimgt.application.extension/src/main/java/org/wso2/carbon/apimgt/application/extension/APIManagementProviderServiceImpl.java

@@ -131,7 +131,7 @@ public class APIManagementProviderServiceImpl implements APIManagementProviderSe
      * {@inheritDoc}
      */
     @Override
-    public ApiApplicationKey generateAndRetrieveApplicationKeys(String apiApplicationName, String tags[],
+    public synchronized ApiApplicationKey generateAndRetrieveApplicationKeys(String apiApplicationName, String tags[],
                                                                 String keyType, String username,
                                                                 boolean isAllowedAllDomains, String validityTime)
             throws APIManagerException {