Restructure top level directory of leap_platform

current test file layout:

* vagrant pre-canned dummy providers
   vagrant/
   Vagrantfile
   hiera.yaml
* `leap test`
   tests/*
* ci tests
   Gemfile
   Gemile.lock
   vendor
   Rakefile
   tests/puppet

proposal:

  provider-tests
    troubleshooting tests run against a live provider via the
    `leap test` command.
  example-provider
    a pre-configured "simulation" provider that can be launched locally without any setup.
  platform-ci
    continuous integration tests for the platform itself.

leap_platform/
  Vagrantfile
  tests/
    README.md
    provider-tests
      helpers/
      whitebox/
      blackbox/
    example-provider/
      vagrant/
      hiera.yaml  -> replaced by other hiera.yaml
    platform-ci/
      provider    (from tests/puppet)
      hiera.yaml  (from tests/puppet)
      Gemfile
      Gemfile.lock
      vendor/
      Rakefile

(from redmine: created on 2016-07-05, closed on 2016-11-08)