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.
