Move PostgreSQL 9.4 real integration tests to Ubuntu 18.04.
Move PostgreSQL 9.4 real integration tests to Ubuntu 18.04.

PostgreSQL 9.4 packages for RHEL 6 were dropped from yum.p.o.

pgbackrest/pgbackrest,pgbackrest/pgbackrest,pgbackrest/pgbackrest,pgmasters/backrest,pgmasters/backrest