rados/singleton-nomsgr: add allocation hint test

Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>
Merge pull request #16 from ceph/wip-hint-tests

rados/singleton-nomsgr: add allocation hint test

Reviewed-by: Sage Weil <sage@inktank.com>
Merge remote-tracking branch 'gh/firefly'