radosgw: create /var/log/radosgw in package, not init script

Fixes: #6475
Signed-off-by: Sage Weil <sage@inktank.com>
ceph.spec.in:  Need to cread radosgw log directory.

Signed-off-by: Gary Lowell  <gary.lowell@inktank.com>
Merge pull request #722 from ceph/wip-6475

radosgw: create /var/log/radosgw in package, not init script

Reviewed-and-tested-by: Gary Lowell <gary.lowell@inktank.com>