Using contain_class instead of include_class

Per rspec-puppet-1.0.1 warning:

DEPRECATION: include_class is deprecated. Use contain_class instead.
Called from .../vendor/gems/rspec-puppet-1.0.1/lib/rspec-puppet/
matchers/include_class.rb:7

Change-Id: I6b410bc4d294bdc6f4feb65a18b213f88b5184f1