Use /etc/sysctl.d on all platforms

The crowbar-hacks cookbook was updated to create a workaround (via cron) on
system that do not support /etc/sysctl.d/ by default.
The old code was in conflict with code from the network barclamp which
unconditionally created /etc/sysctl.d anyway.
Merge pull request #575 from rhafer/fix/sysctl.d-suse

Use /etc/sysctl.d on all platforms