* [Enhance] Sort directories by available space when do trash sweep
In the case when one disk is about to be full, we want to sweep trash
data on this disk as quickly as possible. The currently trash sweep
function is to remove trashed files order by path's name, however, disk
data directories may have some large different available space because
of the load balance algorithm, this patch improve it to remove files by
directories' available space.
* add log
