[CELEBORN-1865] Update master endpointRef when master leader is abnormal

### What changes were proposed in this pull request?
`rpcEndpointRef` should be set to `null` When master leader is not present.

### Why are the changes needed?
Attempt master address index can only be updated when `rpcEndpointRef` is `null`.

The index wont update  if `rpcEndpointRef` has been set but some error ocurs to the master leader.

### Does this PR introduce _any_ user-facing change?
No.

### How was this patch tested?

Closes #3101 from zaynt4606/clb1865.

Authored-by: zhengtao <shuaizhentao.szt@alibaba-inc.com>
Signed-off-by: Shuang <lvshuang.xjs@alibaba-inc.com>

common/src/main/java/org/apache/celeborn/common/client/MasterClient.java

@@ -181,6 +181,7 @@ private boolean shouldRetry(@Nullable RpcEndpointRef oldRef, Throwable e) {
         setRpcEndpointRef(leaderAddr);
       } else {
         LOG.warn("Master leader is not present currently, please check masters' status!");
+        resetRpcEndpointRef(oldRef);
       }
       return true;
     } else if (e.getCause() instanceof IOException || e instanceof RpcTimeoutException) {