bootserver: implement smoke tests as a predefined sequence of log messages

Log messages, sent via fluentd and tagged with puavo-autopilot.smoke,
represent critical stages the autopilot goes through while it
operates. Currently there are three stages:

  1. enter-lightdm
  2. try-lightdm-login
  3. enter-desktop
bootserver: improve smoke test output
ruby-puavobs: add method for querying role IDs per school
ruby-puavobs: add method for creating and adding test users to a school
ruby-puavobs: add method for querying puavoId of a user
ruby-puavobs: add method for removing a user
bootserver: create smoke test users automatically with random credentials
bootserver: just long-line wrapping
bootserver: improve smoke test output
ruby-puavobs: refactor common https connection preparation code