Fix formatting of class name in performance summary

Currently the output for an entry that contains a class name looks like
this:

2x plugin/latency (Optional[com.google.gerrit.server.events.StreamEventsApiListener]) (total: 63ms, avg: 31ms)

Metadata#className returns an Optional<String> and we need to get the
value to prevent that " Optional[...]" is included into the output.

Release-Notes: skip
Change-Id: I4907fe47814e557a3ae86cc05cb032e30dbf4968
Signed-off-by: Edwin Kempin <ekempin@google.com>

Author: EdwinKempin

java/com/google/gerrit/server/logging/PerformanceLogContext.java

@@ -141,7 +141,7 @@ public Optional<String> getPerformanceSummary() {
               ? performanceLogRecord
                   .metadata()
                   .map(Metadata::className)
-                  .map(clazz -> " (" + clazz + ")")
+                  .map(clazz -> clazz.isPresent() ? " (" + clazz.get() + ")" : "")
                   .orElse("")
               : "";
       PerformanceInfo info =