Wrong commit back-ref's timestamp in issues upon push

Summary

Commit mention should be inserted at the timestamp the commit has occured - not the push. See http://gitlabtest.ow2.org/clif/test2/issues/314863

Steps to reproduce

• Update the variable PROCESS_COMMIT_LIMIT to 10000 in git_push_service.rb and restart GitLab

• Create project

• Import existing issues (here it comes from JIRA)

• Initialize the repository with a first push

• Push an existing repository

Example Project

See http://gitlabtest.ow2.org/clif/test2

What is the current bug behavior?

Commit mention timestamp match the push event timestamp.

What is the expected correct behavior?

Commit mention timestamp to match the commit timestamp.

Relevant logs and/or screenshots

See http://gitlabtest.ow2.org/clif/test2

Results of GitLab environment info

Expand for output related to GitLab environment info

System information
System:		Debian 8.9
Current User:	git
Using RVM:	no
Ruby Version:	2.3.5p376
Gem Version:	2.6.13
Bundler Version:1.13.7
Rake Version:	12.1.0
Redis Version:	3.2.5
Git Version:	2.13.6
Sidekiq Version:5.0.4
Go Version:	unknown
GitLab information
Version:	10.1.3
Revision:	e6142bc
Directory:	/opt/gitlab/embedded/service/gitlab-rails
DB Adapter:	postgresql
URL:		http://gitlabtest.ow2.org
HTTP Clone URL:	http://gitlabtest.ow2.org/some-group/some-project.git
SSH Clone URL:	git@gitlabtest.ow2.org:some-group/some-project.git
Using LDAP:	no
Using Omniauth:	no
GitLab Shell
Version:	5.9.3
Repository storage paths:

• default: /var/opt/gitlab/git-data/repositories Hooks: /opt/gitlab/embedded/service/gitlab-shell/hooks Git: /opt/gitlab/embedded/bin/git