Proper selinux logic for Horizon

According to here:
http://docs.puppetlabs.com/learning/variables.html
"all facts are strings, and all non-empty strings,
 including the string "false" . are true"

Checking "if $::selinux" will always return true,
just like (if 'hello':) in python will always return true.

This uses str2bool to ensure that the variable is evaluated as a boolean.

Change-Id: I9489c3bd9a217c80762f5875f026676268572d79

manifests/horizon.pp

@@ -101,7 +101,7 @@ class openstack::horizon (
     api_result_limit      => $api_result_limit,
   }
 
-  if $::selinux and $::selinux != 'false' {
+  if str2bool($::selinux) {
     selboolean{'httpd_can_network_connect':
       value      => on,
       persistent => true,