Test cleanups for chefspec 1.3.0

ChefSpec 1.3.0 allows tests to evaluate guards.  Wired in
this cookbook to use that functionality.  Made tests a
bit clearer, and better utilize the block_storage_stubs.

Change-Id: Ib2e3ee8e00bdc5fb5dcda6b48beb0c405e9d8b92