Use DateTimeUtils.currentTimeMillis() to get current time

This method from joda-time supports replacing the system time provider
with a custom provider for tests. Since it is verbose, and we expect
more related methods, put it in the more succinct TimeUtil.nowMs().

This commit covers the trivial cases in the server side; client-side
code still uses System.currentTimeMillis().

Change-Id: I6c56e8c5bbb0cf7b0271e431d1ebdb532967b9e8

gerrit-sshd/src/main/java/com/google/gerrit/sshd/commands/ShowCaches.java

@@ -26,6 +26,7 @@ import com.google.gerrit.server.cache.h2.H2CacheImpl;
 import com.google.gerrit.server.config.SitePath;
 import com.google.gerrit.server.git.WorkQueue;
 import com.google.gerrit.server.git.WorkQueue.Task;
+import com.google.gerrit.server.util.TimeUtil;
 import com.google.gerrit.sshd.CommandMetaData;
 import com.google.gerrit.sshd.SshDaemon;
 import com.google.inject.Inject;
@@ -59,7 +60,7 @@ final class ShowCaches extends CacheCommand {
   static class StartupListener implements LifecycleListener {
     @Override
     public void start() {
-      serverStarted = System.currentTimeMillis();
+      serverStarted = TimeUtil.nowMs();
     }
 
     @Override
@@ -270,7 +271,7 @@ final class ShowCaches extends CacheCommand {
       return;
     }
 
-    long now = System.currentTimeMillis();
+    long now = TimeUtil.nowMs();
     Collection<IoSession> list = acceptor.getManagedSessions().values();
     long oldest = now;
     for (IoSession s : list) {