I had several successful rebalances, and when I call `rebalancereport` it takes some time to collect info about them.
A possible performance improvement: `rebalancereport` does not call `listpays` for every rebalance one by one, but only once.
In my case, this changes the execution time from ~140 secs to ~7 secs.
When the last `rebalanceall` run terminated silently in the background,
it is still useful to get the ending message of that run.
This change will make the `rebalancestop` method to return the same
'nothing to stop' message plus the rebalanceall_msg when there
was a `rebalanceall` somewhere in the past.
The parameter `maxfeepercent` is rarely changed when using manual rebalances.
However `retry_for` is. Swithcing these parameters gives to option to
easily retry with a higher timeout on the console without naming all
arguments.
A channel can exist without a short_channel_id, in the CHANNELD_AWAITING_LOCKIN state, while the funding transaction is sent but not yet included in a block.
Running `rebalanceall` while opening a channel could throw an exception:
```
2021-02-14T09:31:39 UNUSUAL plugin-rebalance.py: Exception in thread Thread-5:
2021-02-14T09:31:39 UNUSUAL plugin-rebalance.py: Traceback (most recent call last):
2021-02-14T09:31:39 UNUSUAL plugin-rebalance.py: File \"/usr/lib/python3.6/threading.py\", line 916, in _bootstrap_inner
2021-02-14T09:31:39 UNUSUAL plugin-rebalance.py: self.run()
2021-02-14T09:31:39 UNUSUAL plugin-rebalance.py: File \"/usr/lib/python3.6/threading.py\", line 864, in run
2021-02-14T09:31:39 UNUSUAL plugin-rebalance.py: self._target(*self._args, **self._kwargs)
2021-02-14T09:31:39 UNUSUAL plugin-rebalance.py: File \"/home/user/plugins/rebalance/rebalance.py\", line 475, in rebalanceall_thread
2021-02-14T09:31:39 UNUSUAL plugin-rebalance.py: result = maybe_rebalance_once(plugin, failed_pairs)
2021-02-14T09:31:39 UNUSUAL plugin-rebalance.py: File \"/home/user/plugins/rebalance/rebalance.py\", line 443, in maybe_rebalance_once
2021-02-14T09:31:39 UNUSUAL plugin-rebalance.py: result = maybe_rebalance_pairs(plugin, ch1, ch2, failed_pairs)
2021-02-14T09:31:39 UNUSUAL plugin-rebalance.py: File \"/home/user/plugins/rebalance/rebalance.py\", line 425, in maybe_rebalance_pairs
2021-02-14T09:31:39 UNUSUAL plugin-rebalance.py: wait_for_htlcs(plugin, [scid1, scid2])
2021-02-14T09:31:39 UNUSUAL plugin-rebalance.py: File \"/home/user/plugins/rebalance/rebalance.py\", line 384, in wait_for_htlcs
2021-02-14T09:31:39 UNUSUAL plugin-rebalance.py: if scids is not None and channel['short_channel_id'] not in scids:
2021-02-14T09:31:39 UNUSUAL plugin-rebalance.py: KeyError: 'short_channel_id'
```
