Include derby-plugin.jar in docs/examples/varia

When using the Derby DBMS with jboss, the example configuration file in:

JBOSS_HOME\docs\examples\jca\derby-ds.xml

references a Derby MBean:

<mbean code="org.jboss.jdbc.DerbyDatabase" name="jboss:service=Derby" />

This MBean is supposed to properly start and shutdown the embedded Derby instance. It is supposed to be delivered as a jar in JBOSS_HOME\server\default\lib\ along with hsqldb-plugin.jar, for instance, which serves a similar purpose.

Unfortunately the zip/tar.gz download does not appear to contain it, nor the JEMS installer seems to create it, even when configured with Derby instead of HSQL.

Apparently the jar gets built when building jboss in varia/output/lib, but not in the default directory.