core: Create artifact for PostgreSQL module

Currently we are deploying the PostgreSQL module using the "setup"
profile, but we don't have an artifact for the required module. This
patch reuses the module description that we had and uses it to build a
new "dependencies" artifact that can then be easily installed.

Change-Id: Iad7ee2264fde3badf7d242fe3a20874e1d24d6bf
Signed-off-by: Juan Hernandez <juan.hernandez@redhat.com>