Set max_open_files for large clusters

[hufman]

The ansible cookbook defaults to setting max_open_files to 128k. Users of the Chef cookbook can say node['ceph']['config']['global']['max open files'] = 131072, but perhaps this should be the default?
It seems like the setting defaults to whatever ulimit is set to.

[guilhem]

I don't think our cookbook must override any default application setting.
It's too complicated to maintain.
If someone want to share some good experience, he can do a cookbook wrapper :)