ulimit attribute changes ineffective on Debian/Ubuntu installations

[mfischer-zd]

In commit 26f21f9 a file resource was added for /etc/default/riak that sets the ulimit to establish the maximum number of file descriptors used. However, instead of action :create, action :create_if_missing was used. This only creates the file if it's missing; it won't be updated if the value of the attribute changes.