rgw: if formatter gets too much data, print some
rgw: if formatter gets too much data, print some

If the RGW formatter gets too much data, print some data rather than
printing nothing. This is safe because vsnprintf always properly
null-terminates its output.

Signed-off-by: Colin McCabe <7b35906f1d014e74a9dc8c913eb229119df647aa@dreamhost.com>

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