ReconfigurableBase can log sensitive information

ReconfigurableBase will log old and new configuration values, which may cause sensitive parameters (most notably cloud storage keys, though there may be other instances) to get included in the logs.

Given the currently small list of reconfigurable properties, an argument could be made for simply not logging the property values at all, but this is not the only instance where potentially sensitive configuration gets written somewhere else in plaintext. I think a generic mechanism for redacting sensitive information for textual display will be useful to some of the web UIs too.