Remove sysctl configuration, use ferm dependency

Most of ferm and sysctl configuration is now done by 'debops.ferm' role
with enabled packet forwarding.
Rewrite SSH host fingerprint tasks

Management of host fingerprints in '/root/.ssh/known_hosts' file has
been switched from separate files in a directory assembled into a file
to adding the host fingerprints directly into '/root/.ssh/known_hosts'.

Default length of root SSH keys has been increased to 4096 bits.
Send mail from FQDN address instead of 'root'
Merge pull request #3 from drybjed/openvz-updates

OpenVZ updates