client: add ceph.{cluster_fsid/client_id} vxattrs suppport

client: add ceph.{cluster_fsid/client_id} vxattrs suppport

These two vxattrs will only exist in local client side, with which
we can easily know which mountpoint the file belongs to and also
they can help locate the debugfs path quickly.

Fixes: https://tracker.ceph.com/issues/48337
Signed-off-by: Xiubo Li <xiubli@redhat.com>
(cherry picked from commit 5635f25dd4a134f2fb32d2cb9dd73c0e947295e6)

Conflicts:
	src/client/Client.cc
	  - add .hidden member because we still need it
            in nautilus
	src/client/Client.h
	  - drop the mirror.info xattr related code
            because nautilus does not introduce it