Give VM a chance to reject old backup-utils versions

This is a bit of a hack but lets new versions of the VM reject
backup-utils restores if the version is too old. I'd like to move
this into the ghe-host-check negotiation but we need this for
current versions of backup-utils.
Merge pull request #22 from github/ghebuver2

Give VM a chance to reject old backup-utils versions
v2.0 release