Lnd: itest: btcd backend logs not complete

[yyforyongyu]

Because btcd uses logrorate, when the log file size exceeds 10MB, it's compressed and saved as a .gz file, as shown in this line.

On the other hand, in the itest, only the uncompressed logs are saved, as shown in this line.
Debugging itest will sometimes need all the logs.

The logrorate settings should be configured for lnd nodes too, using --maxlogfiles=0 to disable log rotation when running integration tests.

[ErikEk]

I'll take this one.

[ErikEk]

I'll wait for #4617 to be merged.