core: fix drop old uuid functions for pg9.x

In pg9.x we can not drop the functions without dropping first the
extension (uuid-ossp)
This patch adds a DROP EXTENSION of uuid-ossp for pg 9.x

Change-Id: I45ecf68b27cc04d4592b30e23c774b87e451cabc
Signed-off-by: Eli Mesika <emesika@redhat.com>