Improve ChefSpec coverage

The remaining untouched resources are due to a non-existant suse spec.
I.e., the package resources coming from the suse platform_attributes:

  package[openstack-nova]            openstack-compute/recipes/nova-common.rb:33
  package[python-mysql]              openstack-compute/recipes/nova-common.rb:41

and this one, coming from a suse platform_family conditional:

  execute[loading kvm modules]       openstack-compute/recipes/libvirt.rb:103

Change-Id: Ic0bac7c8c1abe52e2e21d1daa71cf5e05f3b8991
Merge "Improve ChefSpec coverage"