Not sure context.xml is supported in JBoss ... You may need to create a jboss.xml or jboss-web.xml instead.
I have created jboss-web.xml and it contains referece (<resource-ref>) to my resource. But it doesn't work.
Problem is with the useNaming attribute in context.xml. It is set to true value by default, enabling the JNDI InitialContext for web applications.
In JBoss source codes is this attribute set to "false" and the resource isn't deployed during the deployment process.