drop mock dependency

mock is not used anywhere in the module, let's drop it.
This patch will help to hit this bug:
https://launchpad.net/bugs/1492636

Change-Id: Id9e7a4a2e7e01f4e5d44da516220b9b3162f6fc7

Gemfile

@@ -14,7 +14,6 @@ group :development, :test do
   gem 'puppet-lint-variable_contains_upcase', :require => 'false'
   gem 'puppet-lint-numericvariable',          :require => 'false'
   gem 'json',                                 :require => 'false'
-  gem 'webmock',                              :require => 'false'
   gem 'puppet-openstack_spec_helper',
       :git => 'https://git.openstack.org/openstack/puppet-openstack_spec_helper',
       :require => false

spec/spec_helper.rb

@@ -1,6 +1,5 @@
 require 'puppetlabs_spec_helper/module_spec_helper'
 require 'shared_examples'
-require 'webmock/rspec'
 
 require 'puppet-openstack_spec_helper/defaults'
 require 'rspec-puppet-facts'