Need postgresql-9.6 on the circleci build container? Here goes

circle.yml

machine:
  pre:
  # custom steps for postgresql-9.6 on circleci build container
    - sudo service postgresql stop
    - sudo apt-get purge -y postgresql*
    - sudo apt-get update
    - sudo apt-get install postgresql lsof
    - sudo mkdir -p /etc/postgresql/9.6/main/
    - >
      sudo cp -v /usr/share/postgresql/9.6/postgresql.conf.sample \
        /var/lib/postgresql/9.6/main/postgresql.conf
    - >
      sudo cp -v /usr/share/postgresql/9.6/pg_hba.conf.sample \
        /var/lib/postgresql/9.6/main/pg_hba.conf
    - >
      sudo cp -v /usr/share/postgresql/9.6/pg_ident.conf.sample \
        /var/lib/postgresql/9.6/main/pg_ident.conf
    - >
      sudo sh -c \
        'echo "local all all trust\n host all all 127.0.0.1/32 trust" > \
        /var/lib/postgresql/9.6/main/pg_hba.conf'
    - sudo sleep 5 && sudo pg_createcluster 9.6 main --start || exit 0
    - sudo psql --version
    - sudo service postgresql restart && sleep 5
    - sudo lsof -PiTCP -upostgres
    - sudo su - postgres -c "echo \"CREATE ROLE root WITH LOGIN SUPERUSER;\" | psql"
    - sudo su - postgres -c "echo \"CREATE ROLE postgres WITH LOGIN SUPERUSER;\" | psql"
    - sudo su - postgres -c "echo \"GRANT ROOT to postgres;\" | psql"
~