Use `git update-ref --stdin -z` to speed up TestEnv.set_repo_refs
Use `git update-ref --stdin -z` to speed up TestEnv.set_repo_refs

Previously, we were calling `git update-ref <ref> <sha>` about 30 times per
test using `create(:project)` or similar.

darkrasid/gitlabhq,darkrasid/gitlabhq,iiet/iiet-git,dreampet/gitlab,iiet/iiet-git,dplarson/gitlabhq,htve/GitlabForChinese,iiet/iiet-git,axilleas/gitlabhq,dplarson/gitlabhq,t-zuehlsdorff/gitlabhq,mmkassem/gitlabhq,openwide-java/gitlabhq,jirutka/gitlabhq,openwide-java/gitlabhq,LUMC/gitlabhq,dreampet/gitlab,dreampet/gitlab,dplarson/gitlabhq,jirutka/gitlabhq,openwide-java/gitlabhq,htve/GitlabForChinese,mmkassem/gitlabhq,daiyu/gitlab-zh,darkrasid/gitlabhq,t-zuehlsdorff/gitlabhq,stoplightio/gitlabhq,htve/GitlabForChinese,axilleas/gitlabhq,stoplightio/gitlabhq,darkrasid/gitlabhq,daiyu/gitlab-zh,t-zuehlsdorff/gitlabhq,stoplightio/gitlabhq,htve/GitlabForChinese,jirutka/gitlabhq,axilleas/gitlabhq,iiet/iiet-git,dplarson/gitlabhq,axilleas/gitlabhq,LUMC/gitlabhq,stoplightio/gitlabhq,daiyu/gitlab-zh,LUMC/gitlabhq,jirutka/gitlabhq,mmkassem/gitlabhq,dreampet/gitlab,mmkassem/gitlabhq,openwide-java/gitlabhq,daiyu/gitlab-zh,LUMC/gitlabhq,t-zuehlsdorff/gitlabhq