librbd: avoid generating ESHUTDOWN in ManagedLock

librbd: avoid generating ESHUTDOWN in ManagedLock

EBLOCKLISTED has a very special meaning but happens to be an alias for
ESHUTDOWN.  If the client gets blocklisted, we always want to propagate
EBLOCKLISTED error code since it's generated by the OSD.

For ManagedLock use case of indicating that an operation on the lock
raced with lock shut down, meaning that a higher level request can just
be restarted, ERESTART should do.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>