tests: fix rkt command environment (#5011)
tests: fix rkt command environment (#5011)

The environment variables needed for envoking `rkt` command line
should include host PATH (to access `iptables`).

Given that the command runs outside the VM, untrusted task environment
variables should NOT be honored here.

We do this already with `rkt`, but the change is quite subtle to miss
when refactoring.
burdandrei/nomad,hashicorp/nomad,hashicorp/nomad,hashicorp/nomad,burdandrei/nomad,burdandrei/nomad,dvusboy/nomad,dvusboy/nomad,hashicorp/nomad,burdandrei/nomad,dvusboy/nomad,burdandrei/nomad,burdandrei/nomad,hashicorp/nomad,dvusboy/nomad,burdandrei/nomad,dvusboy/nomad,dvusboy/nomad,hashicorp/nomad,dvusboy/nomad