unit-test: Set git proxy in docker

Some repos will download externalprojects via git, and it could be
slow in some network environment.

Set git proxy in $HOME/.gitconfig in the docker container so that git
could use the proxy to speedup the download.

Tested: Verify it's faster to run repo-ci on dbus-sensors that downloads
        nlohmann-json project via git. Without this change, it's very
        slow and eventually fails due to timeout.

Signed-off-by: Lei YU <yulei.sh@bytedance.com>
Change-Id: Ifd480dc7d4003ec21251d6077caf33baf3b622ef
1 file changed