Added check before adding postgresql::user

This is to make sure there are no duplicate definitions when creating multiple
databases owned by the same user.

manifests/db.pp

@@ -46,12 +46,14 @@ define postgresql::db (
     require     => Class['postgresql::server'],
   }
 
-  postgresql::database_user { $user:
-    # TODO: ensure is not yet supported
-    #ensure         => present,
-    password_hash   => $password,
-    #provider       => 'postgresql',
-    require         => Postgresql::Database[$name],
+  if ! defined(Postgresql::Database_user[$user]) {
+    postgresql::database_user { $user:
+      # TODO: ensure is not yet supported
+      #ensure         => present,
+      password_hash   => $password,
+      #provider       => 'postgresql',
+      require         => Postgresql::Database[$name],
+    }
   }
 
   postgresql::database_grant { "GRANT ${user} - ${grant} - ${name}":