Log also thread name in the httpd_log

Having thread name in the httpd_log makes it easier to match entries from the
error_log and httpd_log (note that error_log entries already contain the
thread name). With the thread name included in each log entry in the httpd_log
we have more data to match an error to a request than just the timestamp.

Even with the request trace feature [1] this is still useful as we can do more
analysis before we ask the user to reproduce an error using the request trace.

[1] https://gerrit-review.googlesource.com/Documentation/user-request-tracing.html

Change-Id: I60f0fde1c2708bdc56e6ab458d66abee1b9c59aa

java/com/google/gerrit/pgm/http/jetty/HttpLog.java

@@ -72,7 +72,7 @@ class HttpLog extends AbstractLifeCycle implements RequestLog {
             TimeUtil.nowMs(), // when
             Level.INFO, // level
             "", // message text
-            "HTTPD", // thread name
+            Thread.currentThread().getName(), // thread name
             null, // exception information
             null, // current NDC string
             null, // caller location

java/com/google/gerrit/pgm/http/jetty/HttpLogLayout.java

@@ -40,6 +40,11 @@ public final class HttpLogLayout extends Layout {
 
     opt(buf, event, HttpLog.P_HOST);
 
+    buf.append(' ');
+    buf.append('[');
+    buf.append(event.getThreadName());
+    buf.append(']');
+
     buf.append(' ');
     buf.append('-'); // identd on client system (never requested)