gitlab-ci: Initial conversion of Travis CI build to GitLab CI

Migrate all of the logic in our current .travis.yml file to a GitLab CI
config file.  Notable changes are that this will run the jobs on runners
with the "all" tag.  The timeout for a job needs to be configured higher
than normal as we no longer split building the world up into a large
number of small jobs but instead perform one big build job.  We make use
of stages so that we build and run all of the QEMU + test.py tests first
in order to increase the chance that any problems will be found before
starting the final big build.

Signed-off-by: Tom Rini <trini@konsulko.com>