Improve reliability of TestStartStop with none driver

CI: kill VboxHeadless processes, move load warning until after cleanup

Refactor command runner interface, allow stdin writes

CI experiment: Move gvisor testing behind a flag, double timeout

CI: Cut down log noise by just showing problems by default

Set latest_release to v1.5.1

update releases.json to include v1.5.1

macOS install docs: Minikube is a normal Homebrew formula now

Update Makefile and CHANGELOG for v1.5.1

Set Docker open-files limit ( 'ulimit -n') to be consistent with other runtimes

Used fixed uid/gid for the default user account

add generated asset file to gitignore

Refactor to remove opening browser and just return url(s)

Buildroot now defaults to allocating the package users first,
and the defined users later which means they get higher ids.

In order for the default "docker" user to have the uid/gid as
in previous versions, set it explicitly (to the first: 1000)