Install libre2-dev package

Commit 0c3b8fb96 of zuul added a dependency on fb-re2 which requires the
libre2-dev package to build. Ensure the puppet module installs it.

Change-Id: I5e66a5a2176012663add76ea5d68a22b04b93cf9

manifests/init.pp

@@ -161,6 +161,14 @@ class zuul (
         ensure => present,
       }
     }
+
+  } else {
+    # Needed for fb-re2
+    if ! defined (Package['libre2-dev']) {
+      package { 'libre2-dev':
+        ensure => present,
+      }
+    }
   }
 
   user { 'zuul':