This simplifies the "outside" setup quite a bit and gives us the same
tasks container that test runs on the Cockpit CI run under.
This change also implicitly changes the test browser to chromium (which
is no longer an issue — we just use it from the tasks container).
This will allow us to control the value from test plans, in particular
for disabling at least some unexpected message checks for reverse
dependency testing. We don't want to disable unexpected messages
in general for fmf, as we are looking for exactly these in e.g.
selinux-policy reverse dependency tests.
Move from `su` to `runtest`, as with the former it's impossible to plumb
through variables with non-trivial characters, as they cannot be quoted.
Taken from c38692fa4c
Sync some improvements from cockpit-machines:
* Unbreak running `tmt` in local trees with an already existing ./bots
symlink.
* Don't install all NPM packages, only chrome-remote-interface and sizzle.
* Disable detection of affected tests, taking too long for real
projects.
Copy and adjust the browser.sh and run-test.sh scripts from
cockpit-podman, which we have used in Fedora/RHEL dist-git gating and
packit tests for a while.
