Add omnibus-gitlab to the monthly release process
Merge branch 'release/omnibus' into 'master'

Add omnibus-gitlab to the monthly release process

See merge request !997
Put some entries to CHANGELOG

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Merge branch 'master' of dev.gitlab.org:gitlab/gitlabhq