debian: Add /bin to exec path

Some of the tools used by aptitude and apt-key need to run stuff that is in
/bin

manifests/os/debian.pp

@@ -137,7 +137,7 @@ class base::os::debian::apt (
   # Define aptitude update as a command we can run
   exec { 'aptitude update':
     command     => 'aptitude update',
-    path        => '/usr/bin',
+    path        => '/bin:/usr/bin',
     refreshonly => true,
   }