if ftp_proxy/http_proxy/https_proxy standard environment variables available,
pass them to the docker daemon to build images.
this is required when building behind corporate proxy/firewall, but also help
when using local cache server (ie: apt/yum).
Signed-off-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20170306205520.32311-1-f4bug@amsat.org>
Reviewed-by: NFam Zheng <famz@redhat.com>
Signed-off-by: NFam Zheng <famz@redhat.com>