rotating sandbox hosts needs more time to boot

[progrium]

Changes to sandbox hosts will destroy after create, but the hosts will still be booting up. Need some way to delay or better coordinate.

Perhaps a local-exec provisioner that uses kubectl to run a container that waits for the docker socket to come up. Since CI cannot access docker socket, and wouldn't have a private key to SSH.

[progrium]

#15 is a more specific solution