Fix for #4514

Cleaning up warning/error messages for issue #4514.  There are now
log messages when either aptsources.sourceslist or
softwareproperties.ppa fail to import.  There are also clearer
log warnings when trying to use functions from either.
Formatting Fix for #4514

Formatting fix on warning message(s) when python-software-properties
is unavailable.
Merge pull request #4549 from morganfainberg/4514

Addressing issues in #4514