stack/caucase: fix for python3

hashlib.md5 needs bytes, read the file as binary to prevent

    TypeError: Unicode-objects must be encoded before hashing

stack/caucase/buildout.hash.cfg

@@ -15,4 +15,4 @@
 
 [caucase-jinja2-library]
 filename = caucase.jinja2.library
-md5sum = 2e7e61bb0cf41c28d6d811a0283cf03e
+md5sum = 9e64eca810ae0a184917dd466808dc4f

stack/caucase/caucase.jinja2.library

@@ -124,7 +124,7 @@ recipe = plone.recipe.command
 checksum-file = '{{ template }}.md5'
 command =
   set -e
-  md5_current=$(${buildout:executable} -c "import hashlib ; hashlib.md5(open('{{ template }}').read()).hexdigest()")
+  md5_current=$(${buildout:executable} -c "import hashlib ; hashlib.md5(open('{{ template }}', 'rb').read()).hexdigest()")
   md5_old=$([ -f ${:checksum-file} ] && cat ${:checksum-file} || echo none)
   if [ "$md5_current" != "$md5_old" ] || [ ! -f '{{ csr }}' ] || [ ! -f '{{ key }}' ] ; then
     '{{ buildout_bin_directory }}/caucase-rerequest' --template '{{ template }}' --csr '{{ csr }}' --key '{{ key }}'