Stop builds if a build fails

[AlexU-A]

In order to prevent deployments or other build steps, it would be great to have the option to stop the build process upon receiving an error.

Current behavior:
In some cases when a build step fails, for example when a behat test fails, the build process continues to the next step.

Proposed behavior:
Allow a configuration option that denotes when an error in a build step should terminate the process.

[tortillaj]

I think we should expand upon this idea a bit. Additionally, we add lifecycle hooks:

steps:
  .......
after_success:
  - command: .....
after_fail:
  - command: ...

[tizzo]

Worth noting, this was implemented in the long-sitting build-class branch.

[tortillaj]

@tizzo do you happen to remember the status of that branch? I know we still needed to track down a bug, but I don't remember exactly where it was left.

[tizzo]

I tracked down the bug but there are several branches with some debugging code - it needs to be reconciled and a touch more work done to supplant what's in master today. It has a ton of new features though including having task "stacks", which are a list of tasks that run separately but are reported as one unit back to GitHub, marking tasks optional (say on a per-task basis whether to abandon the build if this task fails, defaults true), reporting that a *task* fails without failing the build as a whole, etc.

[ElusiveMind]

Going to review these branches and see if I can get something testable on the lower environment.