[fuel-main] Ability to build ISO through proxy

[Sergey Kulanov]

We need to have an ability to build fuel ISO behind the proxy, probably some simple variable(s) should be added to fuel-main [1], like:

PROXY=server:port

[1] https://github.com/openstack/fuel-main/blob/master/config.mk

[Svetlana Shturm (sshturm)]

We should pass http_proxy and htps_proxy for all commands that are using
 - sudo,
 - chroot,
 - docker (build and run).

[OpenStack Infra (hudson-openstack)]

Related fix proposed to branch: master
Review: https://review.openstack.org/273621

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/273621
Committed: https://git.openstack.org/cgit/openstack/fuel-main/commit/?id=d34ffc13386a5fdb8fa24b424f4df64b97021091
Submitter: Jenkins
Branch: master

commit d34ffc13386a5fdb8fa24b424f4df64b97021091
Author: Sergey Kulanov <email address hidden>
Date: Thu Jan 28 17:14:37 2016 +0200

    Allow to build fuel/fuel-centos-build docker image through proxy

    Building ISO through proxy is possible out of the box by:

     * defining http_proxy variable, for example
        export http_proxy=http://proxy_ip_address:proxy_port
        export https_proxy=https://proxy_ip_address:proxy_port
        export no_proxy=localhost
        make iso \
          PROXY_CONFIG="http_proxy=http://proxy_ip_address:proxy_port \
          https_proxy=https://proxy_ip_address:proxy_port \
          no_proxy=localhost"

     * allowing to bypass http_proxy variable for sudo operations, by
       updating sudoerc configuration file, for example:
          Defaults env_keep += "http_proxy https_proxy no_proxy"

    The only thing which needs to be updated - bypassing proxy for
    docker build operation. This patch introduces this change

    Change-Id: I2b5c7a071bec7448070395f88565701539a9adef
    Related-bug: #1538698