Handle Persister returning TemporaryFailure for new channels

Handle Persister returning TemporaryFailure for new channels

Previously, if a Persister returned a TemporaryFailure error when
we tried to persist a new channel, the ChainMonitor wouldn't track
the new ChannelMonitor at all, generating a PermanentFailure later
when the updating is restored.

This fixes that by correctly storing the ChannelMonitor on
TemporaryFailures, allowing later update restoration to happen
normally.

This is (indirectly) tested in the next commit where we use
Persister to return all monitor-update errors.