Move managing of SSH host keys into a dedicated element.
Because glean doesn't generate SSH host keys anymore, we need to do it
with a systemd script. This is already handled by CentOS / Fedora so
we don't want to add it there.
This was done to address the upstream bug in debian:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=500192
Change-Id: I31ad667672e08350872db21a83445fe0aa7a4a39
Signed-off-by: Paul Belanger <pabelanger@redhat.com>
