Cleanup the code

[rgayon]

• Split tests
• Make tests docstrings more descriptive
• Add end to end tests
• Rename docker_version to storage_version
• Hardcoded strings in tests should all follow the same format

[rgayon]

Better raise exceptions on bad containers IDs:
docker_explorer/lib/container.py
IOError: [Errno 2] No such file or directory: u'/9960bc8da09dec5971de847a48b2522c60d47fd172b0075c428408f672b1e85d/config.v2.json'

[rgayon]

Check why pylint doesn't catch attributes not declared in init

[rgayon]

Now has even more end2end tests, running on Jenkins