upstart/ceph-osd.conf: bump nofile limit up by 10x

This should ensure that we don't hit this limit on all but the very biggest
clusters.  We seen it hit on a ~500 OSD dumpling cluster.

Backport: firefly, dumpling
Signed-off-by: Sage Weil <sage@redhat.com>
Merge pull request #2156 from ceph/wip-upstart-nfile

upstart/ceph-osd.conf: bump nofile limit up by 10x

Reviewed-by: Greg Farnum <greg@inktank.com>