Add create/destroy commands

[robertgzr]

create can be provided with environment variables and flags to generate the kube-spawn environment and writes it to the kube-spawn directory.

destroy stops machines (if they are running) and removes the configuration from the kube-spawn directory.

Also provide a up command to wrap create and start

Depends on #137
Replaces #38

[robertgzr]

Resolved with #161