Use the correct package names on Debian

This also allows using jessie-backports

README.md

@@ -19,6 +19,9 @@ Debian and RedHat based operating systems, although it may work on others.
 On EL (Red Hat, CentOS etc.) systems, the EPEL repository needs to be enabled
 for the Let's Encrypt client package.
 
+On Debian Jessie the module assumes the package certbot is available. This
+package can be found in jessie-backports.
+
 The module can integrate with [stahnma/epel](https://forge.puppetlabs.com/stahnma/epel)
 to set up the repo by setting the `configure_epel` parameter to `true` (the default for RedHat) and
 installing the module.

manifests/params.pp

@@ -14,10 +14,10 @@
     'server' => 'https://acme-v01.api.letsencrypt.org/directory',
   }
 
-  if $::operatingsystem == 'Debian' and versioncmp($::operatingsystemrelease, '9') >= 0 {
+  if $::operatingsystem == 'Debian' and versioncmp($::operatingsystemrelease, '8') >= 0 {
     $install_method = 'package'
-    $package_name = 'letsencrypt'
-    $package_command = 'letsencrypt'
+    $package_name = 'certbot'
+    $package_command = 'certbot'
   } elsif $::operatingsystem == 'Ubuntu' and versioncmp($::operatingsystemrelease, '16.04') >= 0 {
     $install_method = 'package'
     $package_name = 'letsencrypt'

spec/classes/letsencrypt_spec.rb

@@ -183,7 +183,7 @@
       it { is_expected.to compile }
 
       it 'contains the correct resources' do
-        is_expected.to contain_class('letsencrypt::install').with(install_method: 'vcs')
+        is_expected.to contain_class('letsencrypt::install').with(install_method: 'package')
       end
     end
   end