Rewrite GitAccess for gitlab-shell v2

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Update post-receive worker for new format

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Fix post-receive specs

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Fix specs for internal api

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Merge branch 'gitlab-shell-2-0' into 'master'

Modify GitLab to work with gitlab-shell 2.0

Related to #1516

See merge request !1057
Merge branch 'master' of github.com:gitlabhq/gitlabhq