Merge pull request #185 from dalen/retry

Retry package installs

manifests/source.pp

@@ -61,6 +61,8 @@ define apt::source(
       command     => "${provider} -y install ${required_packages}",
       logoutput   => 'on_failure',
       refreshonly => true,
+      tries       => 3,
+      try_sleep   => 1,
       subscribe   => File["${name}.list"],
       before      => Exec['apt_update'],
     }