puppet: Switch removal of MOTD directories for .hushlogin.

Rather than have to keep resolving apt conflicts with the lack of
`/etc/update-motd.d`, have each user disable the motds with a
`.hushlogin` file.

puppet/zulip_ops/manifests/profile/base.pp

@@ -65,15 +65,6 @@ class zulip_ops::profile::base {
 
   zulip_ops::user_dotfiles { 'zulip': }
 
-  # Clear /etc/update-motd.d, to fix load problems with Nagios
-  # caused by Ubuntu's default MOTD tools for things like "checking
-  # for the next release" being super slow.
-  file { '/etc/update-motd.d':
-    ensure  => directory,
-    recurse => true,
-    purge   => true,
-  }
-
   file { '/etc/pam.d/common-session':
     ensure  => file,
     require => Package['openssh-server'],

puppet/zulip_ops/manifests/user_dotfiles.pp

@@ -25,4 +25,16 @@ define zulip_ops::user_dotfiles (
     mode    => '0644',
     source  => 'puppet:///modules/zulip_ops/dotfiles/emacs.el',
   }
+
+  # Suppress MOTD printing, to fix load problems with Nagios caused by
+  # Ubuntu's default MOTD tools for things like "checking for the next
+  # release" being super slow.
+  file { "${homedir}/.hushlogin":
+    ensure  => file,
+    require => User[$user],
+    owner   => $user,
+    group   => $user,
+    mode    => '0644',
+    content => '',
+  }
 }