More accurate "no OS distribution" messaging

[kzantow]

We should revert lowering the "no OS distribution found" message to debug, but change the logic to only show this when we have OS packages without an OS distribution. The idea behind this warning is when importing SBOMs from other vendors which don't have sufficient information for Grype to be able to determine an OS distribution, show a message to the end user an informational message instructing how to get better results.