Base pkg installation on inception VM: Make it compatible with Ubuntu 12.04

This includes not installing mkpasswd (but keeping it installed for 10.04), and adding "-y" to the PPA addition, which was failing due to

    You are about to add the following PPA to your system:
    Mosh is a remote terminal application that supports intermittent connectivity, allows roaming, and provides speculative local echo and line editing of user keystrokes.
    More info: https://launchpad.net/~keithw/+archive/mosh
    Press [ENTER] to continue or ctrl-c to cancel adding it