Fix: crmd: clear remote node transient attributes on disconnect

Previously, transient attributes and LRM history were cleared for
remote nodes only on startup. But if the shutdown attribute were set,
the node couldn't startup, and the attribute couldn't be cleared,
leaving the node down.

Now, they are cleared at remote node stop (clearing at start is
kept, just to be safe).

This with 4c4d8c5 fixes RHBZ#1338623 while preserving the ability
to do graceful stops on remote nodes.