Bootstrap integration tests
This is the first step to have some tests, that we could run against an
MBS instance, to check that it's functionally correct. Ultimately, these
will replace the test scripts (`contrib/test-*`).
This doesn't really do anything yet, but I would like to make sure that
everyone is on the same page regarding how this will be set up.
Signed-off-by: Hunor Csomortáni <csomh@redhat.com>