Provide an internal wrapper for apt commands.
Provide a flag to allow errors to become warnings.

Reduce level of more frequently desired debug messages to seperate them from the noise.
Don't log entry to Configure.

Reduce debug level of package lists to allow them to be inspected with
less noise.

In generate_sources and configure_apt. Handle those undefs.

This could be because they have been renamed (rare) or they are virtual
(common) in both cases when run interactively apt will warn the user:

e.g.
> Note, selecting 'man-db' instead of 'man'

However this warning is supressed when the output is not a TTY so we
have to contrive another means of identifying these cases.