Set config.ssh.insert_key = false in Vagrantfile

[nihilanth41]

This is essentially the same issue as here
I ran into this problem when trying to provision against a custom base box. When building the base box Vagrant (by default) will replace the default insecure ssh key pair. If you then try to provision against the base box it won't be able to authenticate. Setting the config option would disable the first replacement.

Alternatively, could add a note to the README describing the behavior.

[ruebot]

@nihilanth41 I think adding a section to the README is the best course of action here.

[nihilanth41]

Merged #7