ansible-test: add postgresql var file for Ubuntu 18.04 (#50914)

(cherry picked from commit 8c5b2048de)

test/integration/targets/setup_postgresql_db/vars/Ubuntu-18-py3.yml

@@ -0,0 +1,8 @@
+postgresql_packages:
+  - "postgresql"
+  - "postgresql-common"
+  - "python3-psycopg2"
+
+pg_hba_location: "/etc/postgresql/10/main/pg_hba.conf"
+pg_dir: "/var/lib/postgresql/10/main"
+pg_ver: 10