Secrets yml for GitLab CI

Fixes #664

See merge request !409

Check if SElinux is enforced and skip loading module if disabled.

No one supplied MR to solve it so this fixes #501 and confirmed on #660

See merge request !408

Add builds directory configuration for GitLab CI.

Fixes #659

See merge request !407

Set net.core.somaxconn kernel parameter for unicorn

Set net.core.somaxconn kernel parameter to a value equal or higher then unicorn backlog_socket. The default kernel value is 128 which is lower then the default unicorn backlog.

Closes #656

See merge request !405

Add docs about using custom certificate. Fixes #626

See merge request !406

Posttrans for rhel

Different way of handling #649 .

Also fixes #528

See merge request !402

Dont start if path is nonexistent

This should handle #272 .

Even when /opt is mounted as a separate filesystem, systemd will attempt starting GitLab and if for some reason all filesystems are not mounted this will make GitLab start fail.

Fix contains a move of the service file to [the installed packages unit location](http://www.freedesktop.org/software/systemd/man/systemd.unit.html) of `/usr/lib/systemd/system` and also adds a condition to start GitLab only after all system services are loaded.

See merge request !403