HTTP/HTTPS プロキシーを使用している OCP 4.x で toolbox が起動に失敗する

Issue

HTTP_PROXY と HTTPS_PROXY が適切に設定されている場合でも、toolbox は次のエラーで失敗します。

Trying to pull registry.redhat.io/rhel8/support-tools...ERRO[0060] Error pulling image ref //registry.redhat.io/rhel8/support-tools:latest: Error initializing source docker://registry.redhat.io/rhel8/support-tools:latest: pinging docker registry returned: Get https://registry.redhat.io/v2/: dial tcp 104.103.100.204:443: i/o timeout
Failed
Error: error pulling image "registry.redhat.io/rhel8/support-tools": unable to pull registry.redhat.io/rhel8/support-tools: unable to pull image: Error initializing source docker://registry.redhat.io/rhel8/support-tools:latest: pinging docker registry returned: Get https://registry.redhat.io/v2/: dial tcp 104.103.100.204:443: i/o timeout