crimson/osd: ignore exception when stopping osd

OSD::stop() is a top-level method in the sense that it will be called
directly when engine stops. so it should not throw any exceptions.
instead, we will print out the error and ignore the exception if any.

Signed-off-by: Kefu Chai <kchai@redhat.com>

src/crimson/osd/osd.cc

@@ -315,6 +315,8 @@ seastar::future<> OSD::stop()
     return monc->stop();
   }).then([this] {
     return store->umount();
+  }).handle_exception([](auto ep) {
+    logger().error("error while stopping osd: {}", ep);
   });
 }