Env variables to set installation and data directories

WildFly Operator has a need to set the Bootable JAR installation dir and data dir to some specific locations. The way to do it is thanks to Environment variables.
A bootable JAR needs to recognize JBOSS_BOOTABLE_HOME and JBOSS_BOOTABLE_DATA_DIR env variables for the Operator to properly operate with an Image containing a Bootable JAR.