Drop JDBC driver properties

JDBC 4 drivers auto-register through the Java ServiceLoader facility. It
is no longer recommended to load the driver through Class.forName. This
allows us to get rid of all the db.driver properties (which where not DRY
anyway, as the driver identification was duplicated between the driver
property and the url property).

DataNucleus unfortunately insists on loading something, so for the time
being I gave it a dummy class to load (java.lang.String). An upcomming
patch will solve this while moving everything to HikariCP.

The patch marks all *.db.driver properties as obsolete. Use of JDBC 4
compliant drivers is required.

Target: trunk
Require-notes: yes
Require-book: yes
Acked-by: Albert Rossi <arossi@fnal.gov>
Acked-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>
Patch: http://rb.dcache.org/r/6535/