This commit duplicates a small amount of Ruby code that is run at build
or install time. Over time, it would be nice to remove the dependency
on Ruby for these steps, but the focus right now is on run-time.

We'll be removing lib/* from gitlab-shell very soon, and these commands
need to keep working when we do.

This reverts commit a18c90128e4d3eeae1233b1bc3c3998afd223c0d, reversing
changes made to 0a64624152735766c428d1532e434dd0bf5a9748.

By default, RubyGems is enabled, which causes the Ruby interpreter
to load 600+ additional files at startup when gitlab-shell is
designed not to use any external gems.

We can lazily create authorized_keys and set its permissions. This
adds negligible overhead and it allows us to remove a setup step from
GitLab both on source and in omnibus-gitlab.

This reverts commit ae498b6cd4122d3d7f35e6b73b50c53615ca3488, reversing
changes made to 79fdf65c71e90773fbf52d6832b74cf5a7124755.

It is not clear what we need these for anymore. Because these commands
would recurse once through all existing files in all Git repositories,
and then another time through all directories these commands could
take very long on a server with a lot of repositories.

We keep the 'chmod' on config.repos_path, to deny world access to all
files and directories beneath it.