1. Refactoring and specs in the `Uniquify` class.

2. Don't use the `AdvisoryLocking` class. Similar functionality is
provided (backed by Redis) in the `ExclusiveLease` class.

1. Use an advisory lock to guarantee the absence of concurrency in `User.ghost`,
to prevent data races from creating more than one ghost, or preventing the
creation of ghost users by causing validation errors.

2. Use `update_all` instead of updating issues one-by-one.

Signed-off-by: NRémy Coutable <remy@rymai.me>

This hack is needed because of an issue when --follow and --skip
are passed to git log at the same time.

See https://gitlab.com/gitlab-org/gitlab-ce/issues/23062Signed-off-by: NRémy Coutable <remy@rymai.me>

This reverts commit e00fb2bdc2090e9cabeb1eb35a2672a882cc96e9.

# Conflicts:
#	.rubocop.yml
#	.rubocop_todo.yml
#	lib/gitlab/ci/config/entry/global.rb
#	lib/gitlab/ci/config/entry/jobs.rb
#	spec/lib/gitlab/ci/config/entry/factory_spec.rb
#	spec/lib/gitlab/ci/config/entry/global_spec.rb
#	spec/lib/gitlab/ci/config/entry/job_spec.rb
#	spec/lib/gitlab/ci/status/build/factory_spec.rb
#	spec/lib/gitlab/incoming_email_spec.rb

This reverts commit cb10b725c8929b8b4460f89c9d96c773af39ba6b.

This reverts commit 96bef54154e669f9a3e92c3a4bc76c0be3a52e48.

This should solve 99% of the false-positive of the `ee_compat_check` job.