charmloader: log fails to file

Log all charms and bundles that failed the ingestion process. With err descriptions if possible.
The separate logger was intentional to "Log all charms and bundles that failed the ingestion process. With err descriptions if possible." 

1. There is another place in this code which logs an error, and I do feel it is an error, but it is not an error publishing.
2.  We cannot control other loggo loggers, for example juju.charms logger as created and used by juju/charms package. Admittedly, this particular logger never writes at the Error level, but the intent would be lost.

The intent as I understood it was to have a separate log file with only 1 kind of error message. This probably could have been written a little better in the card.

Too many years of log4net, log4j, nlog, python logging for me, I guess.