unify behavior of retrace between distributions between exhaustive and "only directly relevant"

[yarikoptic]

ATM

• conda would provide a full list of pkgs in the environment even when only a single file is "retraced"
• debian/rpm/... would list only the packages containing the files being retraced.

IMHO we should unify, and by default probably be non-exhaustive, while in exhaustive mode providing a full list of pkgs.