Sysctl: make the default priority 70

udp2log broke because the kernel parameters it requires were being clobbered.
This is because both Sysctl::Parameters['big rmem'] and
Sysctl::parameters['wikimedia base'] were set to the default priority of 60,
and each was attempting to set net.core.rmem_max to a different value.

In change I50d929847, Andrew B. and I fixed things by setting the priority on
Sysctl::Parameters['big rmem'] to 70. In hindsight, this doesn't go far enough.
We can safely assume that in case of conflict between 'wikimedia base' and some
other Sysctl::Parameters resource, it's the other resource that should win,
since it is more specific than 'wikimedia base', which specifies cluster-wide
defaults.

Having the default priority set to 60 is unfortunate, because that is the
lowest possible value that is not reserved by Debian/Ubuntu for sysctl configs
bundled with packages, so it doesn't leave room for declaring broad defaults.
So: make the default 70, and change 'wikimedia base' to 60.

Also add documentation and remove the 'filename' parameter from both
Sysctl::Parameters and Sysctl::Conffile, since it is both unnecessary and
leaves a way to circumvent the naming convention.

I tested this on Vagrant. I also confirmed that integer values are
automatically cast to strings for the purpose of regex matching, so a literal
'70' (the number, not the string) does indeed match /^\d?\d$/.

Change-Id: I02673456fdaec1e065dff449a12435c5ecccf14a
Merge "Sysctl: make the default priority 70" into production