Avoid duplicate package swift.

A duplicate can appear if installed on the same node with
openstack::glance with glance_backend=swift, which also installs
this package for client utilities and libraries.

manifests/init.pp

@@ -28,10 +28,12 @@ class swift(
 
   Class['ssh::server::install'] -> Class['swift']
 
+  if !defined(Package['swift']) {
     package { 'swift':
       name   => $::swift::params::package_name,
       ensure => $package_ensure,
     }
+  }
 
   package { 'swiftclient':
     name   => $::swift::params::client_package,