Remove platforms - azure/gcp/govcloud/vmware/openstack

[cpanato]

Cleaning master by removing azure, govcloud, metal, gcp, openstack and vmware.

Those platforms will be readded, when we advance in the new installer flow. For now we are focus on AWS.

[squat]

We also need to modify the rules in examples/BUILD.bazel and Documentation/BUILD.bazel

[cpanato]

@squat it uses the variables.bzl I changed that only. let me know if this is not good

[enxebre]

as we are not supporting track-1 in this branch anymore we can remove bootkube module, rename bootkube-ut2 to bootkube and update the references in the steps folder now.

[enxebre]

• can we also remove modules/openstack?
• Also I'd be in favour of removing non platform specific but unused modules e.g modules/bootstrap-ssh, dns/azure, dns/gcp wdyt?
• In the root BUILD.bazel there's glob pointing to "platforms" folder that should be removed now
• Can we also remove the root Makefile?
• Also modules/ignition can be cleanup now, but let's do that in a different PR

[sym3tri]

@squat I agree with @enxebre

[bluecmd]

FYI, this broke a link on https://coreos.com/tectonic/docs/latest/install/vmware/vmware-terraform.html

Edit the parameters with details of the VMware infrastructure. View all of the VMware specific options and the common Tectonic variables.