Allow a properties file which contains system properties to be loaded in the bootable JAR's entry point

With the fix for generating a logging.properties config there is a chance properties defined in the system-properties or path resource may be needed for the log manager at boot. As part of the mentioned fix a boot-config.properties file will be generated. The entry point of the bootable JAR should look for this file in the $JBOSS_HOME/standalone/configuration directory and if found load those system properties before the log manager is configured.