Fix vcsrepo refresh trigger on non-branch repository

Introduce $askbot_ensure class parameter that defaults to
'present'. This change prevents retriggering of refresh event
by vcsrepo resource when the repo is tied to a specific commit
instead of a branch.

Change-Id: I49ce766c0e085a48a50d41d39b3e57e3e8014979

manifests/init.pp

@@ -81,7 +81,8 @@ class askbot (
   $custom_theme_name            = undef,
   $solr_enabled                 = false,
   $smtp_port                    = '25',
-  $smtp_host                    = 'localhost'
+  $smtp_host                    = 'localhost',
+  $askbot_ensure                = 'present',
 ) {
 
   class { '::askbot::install':
@@ -103,7 +104,7 @@ class askbot (
   }
 
   vcsrepo { "${dist_root}/askbot":
-    ensure   => latest,
+    ensure   => $askbot_ensure,
     provider => git,
     revision => $askbot_revision,
     source   => $askbot_repo,