Fixed #78, connect peers with a barbell topology

[ChihChengLiang]

What was wrong?

Create a python script that generates

• a simple barbell topology, and
• docker exec scripts for containers on all hosts to add peers.

Other:

• Move image build to its one playbook.

To reproduce and review this PR, run ansible-playbook example_run_nodes.yml

How was it fixed?

• Python script generates a topology YAML file like the following example shows.
• The file is later loaded as Ansible variables.
• In cli_addpeer.yml playbook, the hosts run their docker exec commands respectively.

# group_vars/all/topology.yml
ubuntu@18.234.182.34:
- docker exec -t peer_30404 sh -c './sharding-p2p-poc -loglevel=DEBUG -client addpeer 35.173.237.134 30407 30407'
- docker exec -t peer_30405 sh -c './sharding-p2p-poc -loglevel=DEBUG -client addpeer 35.173.237.134 30410 30410'
- docker exec -t peer_30403 sh -c './sharding-p2p-poc -loglevel=DEBUG -client addpeer 18.234.182.34 30406 30406'
- docker exec -t peer_30406 sh -c './sharding-p2p-poc -loglevel=DEBUG -client addpeer 34.229.182.24 30401 30401'
ubuntu@34.229.182.24:
- docker exec -t peer_30400 sh -c './sharding-p2p-poc -loglevel=DEBUG -client addpeer 34.229.182.24 30402 30402'
- docker exec -t peer_30402 sh -c './sharding-p2p-poc -loglevel=DEBUG -client addpeer 18.234.182.34 30404 30404'
- docker exec -t peer_30401 sh -c './sharding-p2p-poc -loglevel=DEBUG -client addpeer 35.173.237.134 30409 30409'
- docker exec -t peer_30399 sh -c './sharding-p2p-poc -loglevel=DEBUG -client addpeer 34.229.182.24 30400 30400'
ubuntu@35.173.237.134:
- docker exec -t peer_30407 sh -c './sharding-p2p-poc -loglevel=DEBUG -client addpeer 35.173.237.134 30408 30408'
- docker exec -t peer_30408 sh -c './sharding-p2p-poc -loglevel=DEBUG -client addpeer 18.234.182.34 30405 30405'
- docker exec -t peer_30410 sh -c './sharding-p2p-poc -loglevel=DEBUG -client addpeer 18.234.182.34 30403 30403'
- docker exec -t peer_30409 sh -c './sharding-p2p-poc -loglevel=DEBUG -client addpeer 34.229.182.24 30399 30399'

Cute Animal Picture

[mhchia]

Traceback (most recent call last):
  File "scripts/topology.py", line 75, in <module>
    with open("group_vars/all/topology.yml", "w") as f:
FileNotFoundError: [Errno 2] No such file or directory: 'group_vars/all/topology.yml'

btw. It seems group_vars/all should be added to git