osd: initialize OSDService::next_notif_id

CID 1019627 (#1 of 1): Uninitialized scalar field (UNINIT_CTOR)
2. uninit_member: Non-static class member "next_notif_id" is not initialized in this constructor nor in any functions that it calls.

Signed-off-by: Sage Weil <sage@inktank.com>
(cherry picked from commit 499edd8bfc355c2d590f5fa1ef197d1ea5680351)
osd: init test_ops_hook

CID 1019628 (#1 of 1): Uninitialized pointer field (UNINIT_CTOR)
2. uninit_member: Non-static class member "test_ops_hook" is not initialized in this constructor nor in any functions that it calls.

Signed-off-by: Sage Weil <sage@inktank.com>
(cherry picked from commit e30a03210c3efb768b1653df5ae58917ef26e579)