Fix selinux unit tests

The selinux test was also failing due to a type issue with the fact
being used (boolean vs string)

Also pin systemd to match rdo for newton.

Change-Id: I36b3b4494f2086daeb574330ce21b19598650aa0
Closes-Bug: #1707243
Closes-Bug: #1710683
(cherry picked from commit f175a6e282)

Puppetfile_extras

@@ -35,7 +35,7 @@ mod 'ntp',
 
 mod 'systemd',
   :git => 'https://github.com/camptocamp/puppet-systemd',
-  :ref => 'master'
+  :ref => 'a0321364514f52a4c110a15afbdad5109d768fe6'
 
 mod 'ssh',
   :git => 'https://github.com/saz/puppet-ssh',

spec/classes/tripleo_selinux_spec.rb

@@ -58,7 +58,7 @@ describe 'tripleo::selinux' do
 
     context 'with selinux disabled' do
       before :each do
-        facts.merge!({ :selinux => 'false' })
+        facts.merge!({ :selinux => false })
       end
 
       let :params do