It is not nice to have both 'GitlabKeys' and 'GitlabKey'. We also do
not need GitlabKey to be a class when it has no state.

Improve authorized_keys check

The old check only looked if authorized_keys exists. With this change, we look
whether we can actually open the file for reading and writing. When this fails
we try to print useful diagnostic information.

See merge request !79

The old check only looked if authorized_keys exists. With this change, we look
whether we can actually open the file for reading and writing. When this fails
we try to print useful diagnostic information.

Manage authorized_keys permissions continuously

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.

See merge request !78

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.