This patch adds some bash helper scripts.
* docker-machine.bash - command completion for docker-machine
* docker-machine-prompt.bash - function for putting the active machine
name in PS1
* docker-machine-wrapper.bash - function wrapper adding an `use`
command that runs `eval $(docker-machine env whatever)` in the
current shell.
Signed-off-by: David M. Lee <dlee@respoke.io>