Plugin does not use the Jenkins proxy server or system proxy server

Hi,

My GCP setup is as follows:

Ubuntu 20.04 running squid3 proxy.

Ubuntu 20.04 configured against squid3 running Jenkins with no external ip.

http proxy is set in Jenkins, so plugins can be downloaded and updated.

If I then try to create a new cloud using google-compute-engine-plugin, I get the following error in the UI

"Could not list regions in project xxx" (where xxx is my project).

If I set 'JAVA_ARGS=-Djava.net.useSystemProxies=true' in /etc/init.d/jenkins then the issue is resolved.