Ship fixed apt sources files for 12.04+

This way we know that multiverse is enabled and that we can install
virtualbox-guest-{x11,dkms}

Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@canonical.com>
Mark 'make clean' as .PHONY

Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@canonical.com>
Fix testing/Vagrantfile

Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@canonical.com>