We will be using a several dozens of parameters to control gitlab
instance. It makes sense not to deviate in such parameters namings and
defaults from omnibus version.

Thus for such parameters - for clarity - we organize a separate file
where we will be keeping them - gitlab-parameters.cfg.

In this patch series all used parameters will be "imported" from
omnibus-gitlab 8.2.3+ce.0-0-g8eda093.

NOTE it is maybe better to try to autogenerate that file from upstream
    omnibus parameters definitions. If time will tell it becomes hard to
    maintain our copy - we'll consider going that way.

/cc @kazuhiko, @jerome