The keytype field is actually `ssh-dss` for DSA keys and they will not
be stored as `id_rsa.pub`.
Note that newer version of ssh actually also support
`ecdsa-sha2-nistp256` and others so it is also misleading to assume the
field always starts with `ssh-`.
Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/875
Provide help for people who aren't SSH-clued by indicating
how to point to key files that have been named something
other than the default. A lot of people seem to assume that
the filename they choose is irrelevant and then wonder why
their private key is not being found by simple 'ssh' commands.