enable proxy for plays only for stackhpc env

Author: sjpb

environments/.stackhpc/inventory/extra_groups

@@ -53,3 +53,8 @@ cluster
 
 [compute_init:children]
 compute
+
+# DO NOT MERGE:
+# turn on proxying for the cluster
+[proxy:children]
+cluster

environments/.stackhpc/inventory/group_vars/all/proxy.yml

@@ -0,0 +1,6 @@
+# DO NOT MERGE:
+# proxy is steveb-dev on sussex-slurm-data: can't use common default, that's hostname which isn't in /etc/hosts
+# TODO: actually need to add username:password@ in here ...
+# TODO: maybe add some quotes to this?
+proxy_http_proxy: "http://{{ hostvars[groups['squid'] | first].ansible_host }}:{{ squid_http_port }}"
+proxy_plays_only: true