gluon-core: ensure kernel.core_pattern is set

/etc/sysctl.conf is not updated correctly on sysupgrades (fixed in master);
explicitly set kernel.core_pattern to ensure corefiles don't clutter the
root filesystem.

package/gluon-core/luasrc/lib/gluon/upgrade/130-core-pattern

+#!/usr/bin/lua
+
+local sysctl = require 'gluon.sysctl'
+
+sysctl.set('kernel.core_pattern', '/tmp/%e.%t.%p.%s.core')