CI: use wheels from infra mirror

If they are available then we do not need to build them. Especially
AArch64 jobs will speedup (once wheels are built).

Change-Id: I79af6c37950e156018a9204fbcc7417cd7d41012
(adapted by hand)

Author: hrw

tests/templates/template_overrides.j2

@@ -6,6 +6,7 @@
 
 ENV PIP_INDEX_URL {{ nodepool_pypi_mirror }}
 ENV PIP_TRUSTED_HOST {{ nodepool_mirror_host }}
+ENV PIP_EXTRA_INDEX_URL {{ nodepool_wheel_mirror }}
 
 RUN echo registry={{ nodepool_npmjs_proxy }} > /etc/npmrc \
     && mkdir -p /usr/etc \

tests/vars/zuul.yml

@@ -8,3 +8,6 @@ nodepool_grafana_proxy: "http://{{ zuul_site_mirror_fqdn }}:8080/grafana/"
 nodepool_cbs_centos_proxy: "http://{{ zuul_site_mirror_fqdn }}:8080/cbs.centos"
 nodepool_oraclelinux_proxy: "http://{{ zuul_site_mirror_fqdn }}:8080/oraclelinux/"
 nodepool_percona_proxy: "http://{{ zuul_site_mirror_fqdn }}:8080/percona"
+
+# NOTE(hrw): wheel cache goes over 80/443 not on 8080
+nodepool_wheel_mirror: "https://{{ zuul_site_mirror_fqdn }}/wheel/{{ ansible_distribution | lower }}-{{ ansible_distribution_version }}-{{ ansible_architecture | lower }}"