Added a pgbouncer container to allow more then 100 simultaneous processes

The docker-compose environment:

• zookernel: the zoo-kernel container built with python, javascript, postgresql, OAS
• pg: the postgresql container with defaut configuration (max_connections=100)
• pgbouncer: the pgbouncer container with max_client_conn=1000

include a python script to test the max_client_conn setting:

` python docker/test_long_process.py 900 `

Patch generated with:

` diff -ruN ../ZOO-Project.orig/ . > ../docker-clean.patch `