Add PostgreSQL dir with socket to Docker container as a volume

Also explicitly set path to pg_dump 9.6 to avoid using old 9.5 postgres
client.

Fixes: PROD-31827

Change-Id: I727073c1caec40f11b87afcd64e31cdc50185a83
diff --git a/defaults/postgresql/init.yml b/defaults/postgresql/init.yml
index e0d3de1..5b0fdea 100644
--- a/defaults/postgresql/init.yml
+++ b/defaults/postgresql/init.yml
@@ -6,4 +6,5 @@
     postgresql_glusterfs_volume_name: postgresql-data
     postgresql_data_mountpoint: /var/lib/postgresql/data
     postgresql_data_directory: ${_param:postgresql_data_mountpoint}/pgdata
+    postgresql_major_version: '9.6'