pool: don't update atime on flush

Motivation:

The onFlush checksum option calculates the checksum before the file is
flushed to tape.  To do this, it must access that file's data.

Currently, that access results in the file's atime being update, despite
this access not involving a client.

Modification:

Instruct the access not to trigger an atime update.

Result:

The checksum policy onFlush no longer triggers an update a file's atime.

Target: master
Request: 5.0
Request: 4.2
Request: 4.1
Request: 4.0
Request: 3.2
Requires-notes: yes
Requires-book: no
Patch: https://rb.dcache.org/r/11504/
Acked-by: Tigran Mkrtchyan

modules/dcache/src/main/java/org/dcache/pool/nearline/NearlineStorageHandler.java

@@ -109,14 +109,14 @@
 import org.dcache.pool.repository.ReplicaDescriptor;
 import org.dcache.pool.repository.ReplicaState;
 import org.dcache.pool.repository.Repository;
+import org.dcache.pool.repository.Repository.OpenFlags;
 import org.dcache.pool.repository.StateChangeEvent;
 import org.dcache.pool.repository.StateChangeListener;
 import org.dcache.pool.repository.StickyChangeEvent;
 import org.dcache.util.CacheExceptionFactory;
 import org.dcache.util.Checksum;
 import org.dcache.vehicles.FileAttributes;
 
-
 import static com.google.common.base.Preconditions.checkArgument;
 import static com.google.common.base.Preconditions.checkNotNull;
 import static com.google.common.collect.Iterables.transform;
@@ -838,7 +838,7 @@ private class FlushRequestImpl extends AbstractRequest<PnfsId> implements FlushR
         public FlushRequestImpl(NearlineStorage nearlineStorage, PnfsId pnfsId) throws CacheException, InterruptedException
         {
             super(nearlineStorage);
-            descriptor = repository.openEntry(pnfsId, NO_FLAGS);
+            descriptor = repository.openEntry(pnfsId, EnumSet.of(OpenFlags.NOATIME));
             infoMsg = new StorageInfoMessage(cellAddress, pnfsId, false);
             infoMsg.setStorageInfo(descriptor.getFileAttributes().getStorageInfo());
             String path = descriptor.getFileAttributes().getStorageInfo().getKey("path");