gitlab: add acceptance testing to system builds

gitlab: add acceptance testing to system builds

As part of migrating things from Travis to GitLab add the acceptance
tests. To do this:

  - rename system1 to system-ubuntu-main
  - rename system2 to system-fedora-misc
  - split into build/check/acceptance
  - remove -j from check stages
  - use artifacts to save build stage
  - add post acceptance template and use

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200701135652.1366-31-alex.bennee@linaro.org>