HBASE-26946 TestRetainAssignmentOnRestartSplitWithoutZk infinite loop (#4344)

Signed-off-by: Xin Sun <ddupgs@gmail.com>
(cherry picked from commit 2622fa05a6)

hbase-server/src/test/java/org/apache/hadoop/hbase/master/TestRetainAssignmentOnRestart.java

@@ -71,6 +71,7 @@ public class TestRetainAssignmentOnRestart extends AbstractTestRestartCluster {
             } catch (IOException e) {
               throw new UncheckedIOException(e);
             }
+            break;
           }
           try {
             Thread.sleep(1000);