Migrate server classes to Flogger

This is the second part of the migration to Flogger. This change
migrates all classes of the 'server' module to Flogger. Classes of the
'httpd' module have been migrated by the predecessor change. Other
modules continue to use slf4j. They should be migrated by follow-up
changes.

During this migration we try to make the log statements more consistent:
- avoid string concatenation
- avoid usage of String.format(...)

Change-Id: I233afc8360af7fef8640394204d0d676cc0d0001
Signed-off-by: Edwin Kempin <ekempin@google.com>

java/com/google/gerrit/server/git/MergeUtil.java

@@ -23,6 +23,7 @@ import com.google.common.collect.FluentIterable;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Iterables;
 import com.google.common.collect.Sets;
+import com.google.common.flogger.FluentLogger;
 import com.google.gerrit.common.FooterConstants;
 import com.google.gerrit.common.Nullable;
 import com.google.gerrit.common.data.LabelType;
@@ -92,8 +93,6 @@ import org.eclipse.jgit.revwalk.RevCommit;
 import org.eclipse.jgit.revwalk.RevFlag;
 import org.eclipse.jgit.revwalk.RevSort;
 import org.eclipse.jgit.revwalk.RevWalk;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
 
 /**
  * Utility methods used during the merge process.
@@ -104,7 +103,7 @@ import org.slf4j.LoggerFactory;
  * {@code BatchUpdate}.
  */
 public class MergeUtil {
-  private static final Logger log = LoggerFactory.getLogger(MergeUtil.class);
+  private static final FluentLogger logger = FluentLogger.forEnclosingClass();
 
   static class PluggableCommitMessageGenerator {
     private final DynamicSet<ChangeMessageModifier> changeMessageModifiers;
@@ -466,7 +465,7 @@ public class MergeUtil {
     try {
       return approvalsUtil.byPatchSet(db.get(), notes, user, psId, null, null);
     } catch (OrmException e) {
-      log.error("Can't read approval records for " + psId, e);
+      logger.atSevere().withCause(e).log("Can't read approval records for %s", psId);
       return Collections.emptyList();
     }
   }
@@ -499,7 +498,7 @@ public class MergeUtil {
     try (ObjectInserter ins = new InMemoryInserter(repo)) {
       return newThreeWayMerger(ins, repo.getConfig()).merge(new AnyObjectId[] {mergeTip, toMerge});
     } catch (LargeObjectException e) {
-      log.warn("Cannot merge due to LargeObjectException: " + toMerge.name());
+      logger.atWarning().log("Cannot merge due to LargeObjectException: %s", toMerge.name());
       return false;
     } catch (NoMergeBaseException e) {
       return false;