Remove unnecessary a+x bit from /var/log/horizon

The /var/log/horizon directory is created with a+x bit but this
permission is not really necessary.

Change-Id: I79a2628e9c262c25fce7a1d0b0dbfc8de62530b4

manifests/wsgi/apache.pp

@@ -225,7 +225,7 @@ class horizon::wsgi::apache (
     owner   => $unix_user,
     group   => $unix_group,
     before  => Service['httpd'],
-    mode    => '0751',
+    mode    => '0750',
     require => Anchor['horizon::config::begin'],
   }