* Moved the `script` and `after_failure` sections of `.travis.yml`
  to extra files in a new `.travis/` folder
* Copy paste `.travis/common.sh` from Alpine's aport. They have neat
  formatting functions in there for folding
* Add a folding block around each script that gets called
* Use native tracebacks in pytest. These are the same as we see when
  pmbootstrap crashes usually, instead of printing out the entire
  function that causes an error. I think this makes the error output
  easier to read.