Add appropriate RSpec mocks to ensure Factor lookups do what we expec…

…t in Jenkins::Plugins

This is required since Facter#value is going to ultimately start using the File
module to dig through the directory structure on disk looking for facts. With
the OpenBSD support this is suddenly a problem as we weren't previously looking
up facts within these unit tests

See also: <https://github.com/jenkinsci/puppet-jenkins/pull/658/files#r85852243>

spec/unit/jenkins_plugins_spec.rb

@@ -24,7 +24,9 @@
 
       before :each do
         Puppet::Jenkins.stub(:home_dir).and_return(home)
-        File.should_receive(:directory?).with(File.join(home, 'plugins')).and_return(dir_exists)
+        plugin_dir = File.join(home, 'plugins')
+        expect(File).to receive(:directory).with(plugin_dir).and_return(dir_exists)
+        expect(Facter).to receive(:value).with(:osfamily).and_return('RedHat').at_least(:once)
       end
 
       context 'and the directory exists' do
@@ -33,7 +35,7 @@
       end
 
       context 'and the directory does not exist' do
-        it { should be false}
+        it { should be false }
       end
     end
   end