Add DB driver to the list of classes to load

The chimera-cli command was overhauled to make it significantly faster.
One technique used was to limit the classes in the classpath to only
those needed.

Unfortunately, this work excluded the database-driver jar. The current
chimera-cli works for system-test, as the plugin mechanism ensures the
database-driver jar is included; however, the PostgreSQL driver is not
included, resulting in chimera-cli no longer working for machines using
PostgreSQL.  The error message is a stack-trace that starts:

[root@bes-srm dcache]# chimera-cli ls /
Exception in thread "main" java.lang.ClassNotFoundException:
org/postgresql/Driver

[reported in user-forum]

Target: master
Request: 2.6
Requires-notes: yes
Requires-book: no
Patch: http://rb.dcache.org/r/5755/
Acked-by: Gerd Behrmann