These classes are not included with binary distribution. You would need to build JBoss from source and find derby-plugin.jar in varia/output/lib.
I am also facing the same problem and after reading the post I build JBoss from source and put derby-plugin.jar in the JBOSS_HOME/server/default/lib folder.
Restarted the server and deployed the application, still getting the same error.
Any help is appreciated.
Thanks in Advance,