ceph: log repository IO error

Motivation:
help debugging

Acked-by: Paul Millar
Target: master, 3.1, 3.0
Require-book: no
Require-notes: no
(cherry picked from commit 73f60de)
Signed-off-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>
(cherry picked from commit ace6b59)
Signed-off-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>

modules/dcache/src/main/java/org/dcache/pool/repository/ceph/CephFileStore.java

@@ -19,6 +19,9 @@
 package org.dcache.pool.repository.ceph;
 
 import com.google.common.primitives.Longs;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 import diskCacheV111.util.PnfsId;
 import java.io.IOException;
 import java.net.URI;
@@ -46,6 +49,8 @@
  */
 public class CephFileStore implements FileStore {
 
+    protected static final Logger LOGGER = LoggerFactory.getLogger(CephFileStore.class);
+
     /**
      * RADOS objects extended attribute name to store creation time.
      */
@@ -246,6 +251,7 @@ public boolean isOk() {
         try {
             rados.statPool(ctx);
         } catch (RadosException e) {
+            LOGGER.error("Repository health check failed: {}", e.toString());
             return false;
         }
         return true;