[CLI Guide] description of vault configuration element should be improved

Link: https://access.redhat.com/documentation/en-us/red_hat_jboss_enterprise_application_platform/7.1/html-single/management_cli_guide/index#config_management_cli

Description of vault configuration element is difficult to understand and it is not clear how to configure it. There are used keywords like code or module which are not defined. vault itself could be defined/explained as well.

There are missing references to the security guide. XML snippet with example of configuration would be helpful as well.