Provide as option synced-folders as way of passing k8s instead of git clone.

[jellonek]

As in subject.
https://www.vagrantup.com/docs/synced-folders/basic_usage.html
https://github.com/vagrant-libvirt/vagrant-libvirt#synced-folders

sync-folders with 9p as driver provides a method to work on k8s sources on host and still have modifications in devbox without need to push/pull to external server. This should greatly improve process of setting up of devbox and would cut off the need to re-download whole k8s source tree after each ./install.sh invocation.

What do you think about this?