Add checkenabled for as7 plugin

[adam-stokes]

as7 should have a checkenabled routine since at the moment it runs with every sosreport iteration. I'm not sure what packages or files to look for in order to determine this.

Thanks

[jhjaggars]

Maybe what should be done here is to factor the get_jboss_home function up a level, that way we can disable the plugin if we don't know where JBOSS_HOME is.