Managing postgres version on ovirt is dangerous.

It requires pg_dump to run the exact same version up to the minor than the pg server. So installation with centralized up to date postgress will need to install yum repository from Postgress and so yum's rpm. For me, it's postgresql94-9.4.11-2PGDG.rhel7.x86_64 :
cat /etc/yum.repos.d/pgdg-94-centos.repo
[pgdg94]
name=PostgreSQL 9.4 $releasever - $basearch
baseurl=https://download.postgresql.org/pub/repos/yum/9.4/redhat/rhel-7.3-$basearch
...


But by doing this, postgresql-jdbc is also coming from the same repo and brake ovirt. It happens to me twice, and I needed to add:
cat /etc/yum.repos.d/pgdg-94-centos.repo
[pgdg94]
...
exclude=postgresql-jdbc

To avoid this problem, two solution:

Provided directly postgresql-jdbc.jar in ovirt's rpm, it's already the case for a lot of them:

lsof -p 12233 | grep REG | grep -e '/usr/share/ovirt-engine/modules/.*\.jar' -e '/usr/share/java/ovirt-engine/.*\.jar' | wc -l
84

Much more than the rpm's provided one:
lsof -p 12233 | grep REG | grep '/usr/share/java/.*\.jar' | grep -v '/usr/share/java/ovirt-engine' | wc -l
26

Another solution is to add in the spec files:
'Requires: postgresql-jdbc < 9.3'

At least it would break during yum upgrade, avoiding fear and despair when oVirt fails to start with a database error.
That solution was proposed by Didi.