Disable SSLv3 by default

This disables SSLv3 by default on all vhosts we create using this module. We should disable SSLv3 support as it is fundamentally flawed, in that the design allows for MitM attacks when invoked in certain ways. In testing, this does as expected.

This relates to https://github.com/alphagov/govuk_mirror-puppet/pull/44, and I think @dcarley might be interested in this. I would still like to deploy the aforementioned PR in the GOV.UK Mirror repository, too.