dist: increase number of open files
dist: increase number of open files

This limit was found to be too low for production environments. It would
be hit at boot, when we're touching a lot of files from multiple shards
before deciding that we don't need them.

Signed-off-by: Glauber Costa <7ba9037b0dd006f9408bd45b94707becd5cd4e87@scylladb.com>
Message-Id: <87bbf43da1a67f5fa6174017205c6ef8bdb0dc3d.1479829232.git.7ba9037b0dd006f9408bd45b94707becd5cd4e87@scylladb.com>

raphaelsc/scylla,duarten/scylla,scylladb/scylla,raphaelsc/scylla,duarten/scylla,avikivity/scylla,scylladb/scylla,avikivity/scylla,raphaelsc/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla,duarten/scylla