(#21087) Debug output for all augeas error nodes

Adds debug output in cases where augeas has error nodes without children. This
specifically addresses the case where an incorrect lens name is specified, and
may provide better output for other cases as well.

Thanks to Jan Vansteenkiste for the implementation of the fix.
Merge pull request #1765 from phinze/21087-no-debug-logging-when-augeas-lens-is-incorrect

(#21087) Debug output for all augeas error nodes