Adding ChefSpec::Converge to spec_helper.rb

Change-Id: I1e6cc97c4ebdf35e3f023d4c6d9c5be4033aab3d
Addresses: blueprint lint-and-unit-testing-for-havana
Change platform? check in template

Rendering this template currently returns a
Chef::Mixin::Template::TemplateError error on the platform? method.  We
could change the method to node.platform? however this then triggers an
FC028 error.

Note that this issue is only encountered when
node[openstack][block-storage][volume][create_volume_group] set to
true.

Change-Id: I4d5ce97762c6b82bbf10e8194c482049eb3a6620
Closes-Bug: #1280285
Merge "Adding ChefSpec::Converge to spec_helper.rb"