Move ansible version requirements to Vagrantfile for better UX

[oxyc]

Feature discussed in #1070 (comment).

Example if requirement would be 2.3:

drupal-vm cindy@cindy ansible-min-version*: vagrant status
/Users/cindy/Projects/Personal/drupal-vm/Vagrantfile:146:in `block in <top (required)>': You must update Ansible to at least 2.3 to use this version of Drupal VM. (RuntimeError)
	from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/config/v2/loader.rb:37:in `call'
	from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/config/v2/loader.rb:37:in `load'
	from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/config/loader.rb:113:in `block (2 levels) in load'
	from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/config/loader.rb:107:in `each'
	from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/config/loader.rb:107:in `block in load'
	from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/config/loader.rb:104:in `each'
	from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/config/loader.rb:104:in `load'
	from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/vagrantfile.rb:28:in `initialize'
	from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/environment.rb:746:in `new'
	from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/environment.rb:746:in `vagrantfile'
	from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/environment.rb:492:in `host'
	from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/environment.rb:214:in `block in action_runner'
	from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/action/runner.rb:33:in `call'
	from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/action/runner.rb:33:in `run'
	from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/environment.rb:479:in `hook'
	from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/environment.rb:728:in `unload'
	from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/bin/vagrant:177:in `ensure in <main>'
	from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/bin/vagrant:177:in `<main>'

[geerlingguy]

Thanks, this is perfect!