setuptools: Install python-dateutil before setuptools_scm

Latest zc.buildout 2.7.1+slapos013 does not need this customisation but old
rojects still need this patch.

See
nexedi/slapos@6e491a6b
nexedi/slapos@f1e7230e

software/neoppod/software-common.cfg

@@ -42,6 +42,7 @@ environment = neoppod-setup-env
 [neoppod]
 recipe = zc.recipe.egg
 eggs = neoppod[admin, ctl, master, storage-mysqldb]
+  ${python-dateutil:egg}
   ${cython-zstd:egg}
   ${msgpack-python:egg}
   ${python-mysqlclient:egg}

stack/slapos.cfg

@@ -93,10 +93,16 @@ eggs =
   ${python-PyYAML:egg}
   ${python-cliff:egg}
   ${python-cryptography:egg}
+  ${python-dateutil:egg}
   pyOpenSSL
   slapos.cookbook
   slapos.libnetworkcache
 
+[python-dateutil]
+recipe = zc.recipe.egg:custom
+egg = ${:_buildout_section_name_}
+setup-eggs = setuptools_scm
+
 [versions]
 setuptools = 33.1.1
 # Use SlapOS patched zc.buildout