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/GarbageCollectionLogFile.java

@@ -14,6 +14,7 @@
 
 package com.google.gerrit.server.git;
 
+import com.google.common.flogger.backend.Platform;
 import com.google.gerrit.extensions.events.LifecycleListener;
 import com.google.gerrit.server.config.GerritServerConfig;
 import com.google.gerrit.server.config.SitePaths;
@@ -40,13 +41,17 @@ public class GarbageCollectionLogFile implements LifecycleListener {
 
   @Override
   public void stop() {
-    LogManager.getLogger(GarbageCollection.class).removeAllAppenders();
-    LogManager.getLogger(GarbageCollectionRunner.class).removeAllAppenders();
+    getLogger(GarbageCollection.class).removeAllAppenders();
+    getLogger(GarbageCollectionRunner.class).removeAllAppenders();
   }
 
   private static void initLogSystem(Path logdir, boolean rotate) {
-    initGcLogger(logdir, rotate, LogManager.getLogger(GarbageCollection.class));
-    initGcLogger(logdir, rotate, LogManager.getLogger(GarbageCollectionRunner.class));
+    initGcLogger(logdir, rotate, getLogger(GarbageCollection.class));
+    initGcLogger(logdir, rotate, getLogger(GarbageCollectionRunner.class));
+  }
+
+  private static Logger getLogger(Class<?> clazz) {
+    return LogManager.getLogger(Platform.getBackend(clazz.getName()).getLoggerName());
   }
 
   private static void initGcLogger(Path logdir, boolean rotate, Logger gcLogger) {