Split lambda instance creation into functions. create_cluster function
creates a cluster using provisioner, while run_playbook function runs
ansible playbooks, using an ansible manager object given as argument.
Lambda instance creation celery task then sequentially calls the
functions necessary for the complete lambda instance creation.

Other tasks:
- Refactor instance creation function and library names
- Create playbook that waits for ssh, then install proxy
- Update create lambda instance api documentation