crimson/osd: shutdown services in the right order

crimson/osd: shutdown services in the right order

we should stop config service *after* osd is stopped, as osd depends on
a working and alive config subsystem when stopping itself. for instance,
the destructor of AuthRegistry unregisters itself from the ObserverMgr,
which is in turn a member variable of ConfigProxy, so if ConfigProxy is
destroyed before we destroy mon::Client, we will have a segfault with
following backtrace

ObserverMgr<ceph::md_config_obs_impl<ceph::common::ConfigProxy>
>::remove_observer(ceph::md_config_obs_impl<ceph::common::ConfigProxy>*)
at /var/ssd/ceph/build/../src/common/config_obs_mgr.h:78
AuthRegistry::~AuthRegistry() at
/var/ssd/ceph/build/../src/crimson/common/config_proxy.h:101
 (inlined by) AuthRegistry::~AuthRegistry() at
/var/ssd/ceph/build/../src/auth/AuthRegistry.cc:28
ceph::mon::Client::~Client() at
/var/ssd/ceph/build/../src/crimson/mon/MonClient.h:44
ceph::mon::Client::~Client() at
/var/ssd/ceph/build/../src/crimson/mon/MonClient.h:44
OSD::~OSD() at /usr/include/c++/9/bits/unique_ptr.h:81

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