Add allow_hosts to pydistutils.cfg

This should cause easy_install to only contact our pypi mirrors
when fetching packages.

https://pythonhosted.org/setuptools/easy_install.html#restricting-downloads-with-allow-hosts

Change-Id: I7f7847721c2e8c6299c7fe5ab20045e8bdbc5bd7

nodepool/scripts/configure_mirror.sh

@@ -25,6 +25,7 @@ sudo sed -i -e "s,^index-url = .*,index-url = $NODEPOOL_PYPI_MIRROR," /etc/pip.c
 cat >/home/jenkins/.pydistutils.cfg <<EOF
 [easy_install]
 index_url = $NODEPOOL_PYPI_MIRROR
+allow_hosts = *.openstack.org
 EOF
 
 # Double check that when the node is made ready it is able