gitlab-ci: move sdist test run to new fedora job

A full run of the test suite takes quite a bit of time.  This removes one
of the 3 runs from the main 'tests' job, and puts it into the Fedora job.
That test run is mostly to make sure the setup.py and source tarball are
correctly, so that doesn't affect merge requests very often.

This also tests `pip install --user`, which was not really being tested
before.
2 jobs for gitlab-ci-testing-xenial-fedora in 22 minutes and 18 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #43449318
metadata_v0

00:04:09

passed #43449317
test

00:22:18