Adding ChefSpec Custom Matchers for register LWRP

Replaced all lwrp testing in spec/registration_spec.rb with testing via
custom matchers. Also added test for :service_create call in
recipes/registration.rb.

Change-Id: I877b3f5b48fe5b85d9b7825ce5c20e16b157d531
Closes-Bug: #1253016
Addresses: blueprint chefspec-lwrp-for-identity
Merge "Adding ChefSpec Custom Matchers for register LWRP"