Add support for creating and auto-discovering JBoss AS "user instances"

The Fedora JBoss AS package supports creating user instances of JBoss AS. A user instance allows an unprivileged user to run JBoss AS out of that user's home directory. An instance is created using the jboss-as-cp script. For example:

jboss-as-cp -l $HOME/applications/jboss-as-user-instance

The user instance is skinny, meaning it only contains the configuration files for the instance. The libraries are kept in the system instance and referenced by the custom startup script:

JBOSS_BASE_DIR=$HOME/applications/jboss-as-user-instance /usr/share/jboss-as/bin/standalone.sh -c standalone-web.xml

JBoss Tools does not currently auto-detect these instances. However, it could offer to create and/or auto-discover them.

It's possible to get JBoss Tools to control the user instance, but it requires tweaking the startup flags in the server configuration. Here's how:

1. Have JBoss AS auto-discover the system instance at /usr/share/java
2. Open the server launch configuration
3. Uncheck the box "Always update arguments related to the runtime" so our changes don't get overwritten
4. Replace the VM arguments that contain "jboss" with:

-Dorg.jboss.boot.log.file=${env_var:HOME}/applications/jboss-as-user-instance/log/boot.log -Dlogging.configuration=file:${env_var:HOME}/applications/jboss-as-user-instance/configuration/logging.properties -Djboss.home.dir=/usr/share/jboss-as -Djboss.server.base.dir=${env_var:HOME}/applications/jboss-as-user-instance

Having native support for JBoss AS to auto-detect and configure user instances would be ideal.

If changes are required in the jboss-as-cp script, please use this issue tracker: https://bugzilla.redhat.com/buglist.cgi?component=jboss-as&product=Fedora&list_id=455824