Add proxy setting for container image build scripts

[zhipeng liu]

Users in some places like China need to use proxy during building container image.
So it is better to let user be able to add these proxy arguments.

[Ghada Khalil (gkhalil)]

Marked for stx.5.0 / med priority - would be nice to fix to unblock community members in china

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/730566
Committed: https://git.openstack.org/cgit/starlingx/root/commit/?id=bb472a9f37b5acb5c8bf1544f854584f90b5dd88
Submitter: Zuul
Branch: master

commit bb472a9f37b5acb5c8bf1544f854584f90b5dd88
Author: Liu, ZhipengS <email address hidden>
Date: Mon May 25 15:16:43 2020 +0800

    Add proxy setting for container image build scripts

    Users in some places like China need to use proxy during building image.
    So, it is better to let user be able to use proxy by adding these proxy
    arguments.

    Closes-bug: 1890383

    Change-Id: If9ef7d09a5f53148252b4ab62c40ab0f143e1c3f
    Signed-off-by: Liu, ZhipengS <email address hidden>

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/748142

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/748142
Committed: https://git.openstack.org/cgit/starlingx/root/commit/?id=3f9912bd5313e986229d795d80d3bc7d45762e98
Submitter: Zuul
Branch: master

commit 3f9912bd5313e986229d795d80d3bc7d45762e98
Author: zhipengl <email address hidden>
Date: Thu Aug 27 01:46:21 2020 +0800

    Fix the bug introduced by adding proxy for image build scripts

    Below commit will introduce a bug in image build script.
    bb472a9f37b5acb5c8bf1544f854584f90b5dd88

    Closes-bug: 1890383

    Change-Id: I6551a33bf099549eb9a66a65730b884c4a85baef
    Signed-off-by: zhipengl <email address hidden>