Fix #16 by specifying VENV_PATH when running letsencrypt.

Issue copy-paste from
#16

When you install letsencrypt using the VCS method, it will create a
virtualenv, which would normally be located in
~/.local/share/letsencrypt:

Excerpt from letsencrypt-auto:
```
XDG_DATA_HOME=${XDG_DATA_HOME:-~/.local/share}
VENV_NAME="letsencrypt"
VENV_PATH=${VENV_PATH:-"$XDG_DATA_HOME/$VENV_NAME"}
```
However, puppet exec's will not set $HOME, which will stop Debian's
/bin/sh, dash, from expanding ~, so it creates a literal '~' folder.

manifests/certonly.pp

@@ -51,22 +51,25 @@
   $command = "${command_start}${command_domains}${command_end}"
   $live_path = inline_template('/etc/letsencrypt/live/<%= @domains.first %>/cert.pem')
 
+  $venv_path_var = "VENV_PATH=${letsencrypt::venv_path}"
   exec { "letsencrypt certonly ${title}":
-    command => $command,
-    path    => $::path,
-    creates => $live_path,
-    require => Class['letsencrypt'],
+    command     => $command,
+    path        => $::path,
+    environment => [$venv_path_var],
+    creates     => $live_path,
+    require     => Class['letsencrypt'],
   }
 
   if $manage_cron {
     $renewcommand = "${command_start}--keep-until-expiring ${command_domains}${command_end}"
     $cron_hour = fqdn_rand(24, $title) # 0 - 23, seed is title plus fqdn
     $cron_minute = fqdn_rand(60, $title ) # 0 - 59, seed is title plus fqdn
     cron { "letsencrypt renew cron ${title}":
-      command => $renewcommand,
-      user    => root,
-      hour    => $cron_hour,
-      minute  => $cron_minute,
+      command     => $renewcommand,
+      environment => $venv_path_var,
+      user        => root,
+      hour        => $cron_hour,
+      minute      => $cron_minute,
     }
   }
 }

manifests/init.pp

@@ -42,6 +42,7 @@
 class letsencrypt (
   $email               = undef,
   $path                = $letsencrypt::params::path,
+  $venv_path           = $letsencrypt::params::venv_path,
   $repo                = $letsencrypt::params::repo,
   $version             = $letsencrypt::params::version,
   $package_ensure      = $letsencrypt::params::package_ensure,
@@ -81,6 +82,7 @@
   exec { 'initialize letsencrypt':
     command     => "${command} -h",
     path        => $::path,
+    environment => ["VENV_PATH=${venv_path}"],
     refreshonly => true,
   }
 }

manifests/params.pp

@@ -8,6 +8,7 @@
   $package_ensure      = 'installed'
   $config_file         = '/etc/letsencrypt/cli.ini'
   $path                = '/opt/letsencrypt'
+  $venv_path           = '/opt/letsencrypt/.venv' # virtualenv path for vcs-installed letsencrypt
   $repo                = 'git://github.com/letsencrypt/letsencrypt.git'
   $version             = 'v0.4.0'
   $config              = {