engine: upgrade postgres jdbc

- Upgrades PostgreSQL JDBC to version 9.1-901.jdbc4
- Removed postgresql.version from the pom, it was redundant with
  postgres.jdbc.version

Change-Id: I57065e43dee7fcae363174750a959757f438d915
Signed-off-by: Laszlo Hornyak <lhornyak@redhat.com>