deploy-test: "Backport" commit "PyPI is changing"

Extended KVM SR does not have this hosts in allowed, and we need to stick
with it.

For reference in case if some existing Python distribution does not install,
it was detected with "git diff 8deeab.. -- stack/slapos.cfg"

software/erp5testnode/testsuite/deploy-test/software.cfg

 [buildout]
 extends = https://lab.nexedi.com/nexedi/slapos/raw/8deeab28fb7d4fd527c2df05f74fcaf27c8df218/software/kvm/software.cfg
 
+# PyPi servers from new host since some time and change is not incorporated in extended KVM SR
+allow-hosts +=
+  files.pythonhosted.org
+
 parts =
   eggs
   template-deploy-test