Fix buddy env variable names

[penx]

• BUDDY_PROJECT_NAME (e.g. 'my-project') => BUDDY_REPO_SLUG (e.g. 'me/my-project')
• BUDDY_EXECUTION_REVISION_URL (url to commit) = BUDDY_EXECUTION_URL (url to job)

[kuldeepkeshwar]

@penx it would be great if you can update tests too

[penx]

This is a correction to #37 and I'm not sure there are any tests that can be updated, or what a relevant test would look like