vmtest provided pid 1 should respect host $PATH

[danobi]

init.sh hardcodes a standard PATH: https://github.com/danobi/vmtest/blob/5c08c6fd3d9ecad052312d79657e758bbb891287/src/init/init.sh#L18

This works fine most of the time, but not for nix/nixos b/c there's nothing except bash inside standard PATH.

init.sh should inherit host PATH. We can just templatize it like command.template.