Rename `-expect` to `-bootstrap-expect`

[mitchellh]

@armon and I talked about this privately, but we need to rename -expect to -bootstrap-expect. Although it isn't obvious even in the latter case what it exactly does, it is obvious and clear that it is related to bootstrapping and should therefore probably only apply to servers. We concluded that -expect is too vague for something we'll need to support forever.

This must happen prior to 0.4