[mattbostock] Install libxml2 from homebrew

Because Nokogiri needs version 2.6.21 or later of libxml2.
Remove box-templates repo

It's been moved to the attic.
Remove boxes repo
Remove boxgrinder-appliances repo
Remove boxmaker repo

It's been moved to the attic.
Remove machine-bootstrap repo
Remove vcloud-provisioner repo

It's been moved to the attic.

/cc @samjsharpe
Remove vcloud-templates repo

The 'vagrant-govuk' repo no longer uses it as of
alphagov/vagrant-govuk@530ff06da4142f7739dce2d64fa6cbd74eaac7bd.

We're now using 'govuk-provisioning' to provision GOV.UK VMs.

/cc @samjsharpe @robyoung @alexmuller
Remove old vcloudtools repo

It has been superseded by the [vCloud
Tools](http://gds-operations.github.io/vcloud-tools/) gems.

/cc @jabley
Remove vcloud-provisioner from Sam's manifest

It's deprecated.
Remove old vcloudtools repo from James' manifest

It's deprecated.
Remove vcloud-templates from personal manifests

It's deprecated.
Revert "Remove boxes repo"

This reverts commit 31e01888ae64f9890f3654e0085af160caec2ab2.

We use this repo to build the template for the development VM in the
gds/puppet repo.