refs #7970 - don't let Ruby alternative switch to 1.9 on Ubuntu 12.04

Ensures other applications, including hammer, work as 1.8's the expected
default version.

Needs https://github.com/theforeman/foreman-packaging/pull/398

Needs https://github.com/adrienthebo/puppet-alternatives/pull/17, so https://github.com/theforeman/foreman-installer/pull/129 updates foreman-installer.