Allow specifying repo ref as a class parameter

Having to create a custom fact to set project_config ref could be an
overkill for some use cases, e.g. for setting up a third-party CI.

Change-Id: I9772e10a3a56f900e56d425fe7bbfd2261360c1a

manifests/init.pp

@@ -17,24 +17,25 @@
 
 class project_config(
   $url,
+  $revision = 'master',
   $base = undef,
 ) {
 
   $config_dir = Vcsrepo['/etc/project-config']
 
-  # Note project_config_ref is expected to be provided by facter
-  # if you want to use it.
+  # Note project_config_ref can be provided by facter if you want to use it.
   if ($::project_config_ref != undef) {
-    $revision = $::project_config_ref
-  } else {
-    $revision = 'master'
+    $_revision = $::project_config_ref
+  }
+  else {
+    $_revision = $revision
   }
 
   if (!defined($config_dir)) {
     vcsrepo { '/etc/project-config':
       ensure   => latest,
       provider => git,
-      revision => $revision,
+      revision => $_revision,
       source   => $url,
     }
   }