[HOTFIX][YARN] Fix yarn cluster mode fire and forget regression

## What changes were proposed in this pull request?

Fire and forget is disabled by default, with this patch #10205 it is enabled by default, so this is a regression should be fixed.

## How was this patch tested?

Manually verified this change.

Author: jerryshao <sshao@hortonworks.com>

Closes #11577 from jerryshao/hot-fix-yarn-cluster.

yarn/src/main/scala/org/apache/spark/deploy/yarn/Client.scala

@@ -89,7 +89,7 @@ private[spark] class Client(
       }
     }
   }
-  private val fireAndForget = isClusterMode && sparkConf.get(WAIT_FOR_APP_COMPLETION)
+  private val fireAndForget = isClusterMode && !sparkConf.get(WAIT_FOR_APP_COMPLETION)
 
   private var appId: ApplicationId = null