De-flake TestBlockScanner#testSkipRecentAccessFile

[ERROR] testSkipRecentAccessFile(org.apache.hadoop.hdfs.server.datanode.TestBlockScanner)  Time elapsed: 3.936 s  <<< FAILURE![ERROR] testSkipRecentAccessFile(org.apache.hadoop.hdfs.server.datanode.TestBlockScanner)  Time elapsed: 3.936 s  <<< FAILURE!java.lang.AssertionError: Scan nothing for all files are accessed in last period. at org.junit.Assert.fail(Assert.java:89) at org.apache.hadoop.hdfs.server.datanode.TestBlockScanner.testSkipRecentAccessFile(TestBlockScanner.java:1015) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498)