Add support for proxy networks & cleanup playbook vars

roles/llvm/tasks/Ubuntu.yaml

@@ -57,6 +57,7 @@
   get_url:
     url: https://apt.llvm.org/llvm-snapshot.gpg.key
     dest: '{{keyring}}'
+  environment: '{{proxy_environment}}'
 
 - name: add upstream deb repository
   become: true