Some serious log messages don't have id to identify them

As a part of logging unification tests for EAP I found:
modcluster/core/src/main/java/org/jboss/modcluster/load/metric/impl/AverageSystemLoadMetric.java

• 52 logger.warnf("%s is not supported on this system and will be disabled.", this.getClass().getSimpleName());
  modcluster/core/src/main/java/org/jboss/modcluster/load/metric/impl/SystemMemoryUsageLoadMetric.java
• 64 this.logger.warn(this.getClass().getSimpleName() + " requires com.sun.management.OperatingSystemMXBean.");

these should be moved to ModClusterLogger.java as well

(See BZ: 1008901)