radosgw: shut down threadpool
radosgw: shut down threadpool

Don't crash when run as a non-daemon without apache.. e.g. 'radosgw' with
no args.

Fixes: #1572
Signed-off-by: Sage Weil <6dd34506bbd5e58221bbb3e4732d97c91f02277b@newdream.net>

ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph