There are currently 4 different ways to run garbage collection using
lix:
- `nix-collect-garbage`
- `nix-store --gc`
- `nix store gc`
- (using the daemon directly)
As they were written all at different times, their output varies (and is
broken in some case). This unifies the display of informations in the
following ways:
- The list of paths in the results is always printed (in the nix3 cli it
is hidden unless `-v` is passed)
- The number of paths in the result set is always displayed
- The size of deleted paths is only shown when actually deleting things
(as it would have been 0B in any case)
Fixes#905
Change-Id: I40d9ec7c6d76795f6c6dd30df196d1e855bdb9db