build-unit-test-docker: Use proxy and apt mirror

When http_proxy environment is set, use the proxy while building the
docker image.
When UBUNTU_MIRROR is set, use apt mirror to speed up the apt downloads.

Signed-off-by: Lei YU <yulei.sh@bytedance.com>
Change-Id: I286e7e26f3639af93caa95195023b14ad296f83e
1 file changed