Fix for failing TestFsDatasetImpl#testCleanShutdownOfVolume

TestFsDatasetImpl#testCleanShutdownOfVolume fails very often.
We added more debug information in HDFS-10260 to find out why this test is failing.
Now I think I know the root cause of failure.
I thought that LocatedBlock#getLocations() returns an array of DatanodeInfo but now I realized that it returns an array of DatandeStorageInfo (which is subclass of DatanodeInfo).
In the test I intended to check whether the exception contains the xfer address of the DatanodeInfo. Since DatanodeInfo#toString() method returns the xfer address, I checked whether exception contains DatanodeInfo#toString or not.
But since LocatedBlock#getLocations() returned an array of DatanodeStorageInfo, it has storage info in the toString() implementation.