Build existing rbenv rubies for trusty

I'm currently building and uploading all of these to the [test ppa](https://launchpad.net/~gds/+archive/ubuntu/test-govuk/+packages).

Note: this deliberately omits 2.0.0-p247 because we're no longer using it[1].  I'll issue a separate PR to clean it up.

[1] https://github.gds/gds/puppet/pull/2151