Sysctl update to 0.6.0

Update sysctl to current release 0.6.0.
This requires an api change: including recipe "sysctl" => "sysctl:apply". This makes it incompatible with releases <0.6.0.

Thanks to @rmoriz for pointing to the outdated version in #44!

One more thing to clear: I don't know whether we should make this into a conditional, i.e. support sysctl <0.6.0 and >= 0.6.0. It's certainly possible to get the deployed cookbook version and run internals for version comparison (since chef provides methods for both).

Let's clear this before merging.