crimson/mon:use shared_future for waiting MauthReply

crimson/mon:use shared_future for waiting MauthReply

when monitor-side close the connection, msgr call MonClient
ms_handle_reset cause reply.get_future be called twice then
assert happen in promise.get_future.
promise<T...>::get_future() noexcept {
    assert(!this->_future && this->_state && !this->_task);
    return future<T...>(this);
}
use shared_promise instead of promise to solve it.

Signed-off-by: chunmei Liu <chunmei.liu@intel.com>