change the agent log level to millisecond (#1580)

* Fix bug stop stopSpan when not createSpan

* Fix bug stop stopSpan when not createSpan

* change the agent log level to millisecond

apm-sniffer/apm-agent-core/src/main/java/org/apache/skywalking/apm/agent/core/logging/core/EasyLogger.java

@@ -66,7 +66,7 @@ public class EasyLogger implements ILog {
 
     String format(LogLevel level, String message, Throwable t) {
         return StringUtil.join(' ', level.name(),
-            new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date()),
+            new SimpleDateFormat("yyyy-MM-dd HH:mm:ss:SSS").format(new Date()),
             targetClass.getSimpleName(),
             ": ",
             message,