Incorrect disk space calculation inside docker container

[ikopylov]

Looks like we should use frsize instead of bsize here: https://github.com/qoollo/bob/blob/master/bob/src/hw_metrics_collector.rs#L169. But this should be tested.

Statvfs struct declaration: https://man7.org/linux/man-pages/man3/statvfs.3.html

Here is the issue for MacOs: docker/for-mac#2136

[ikopylov]

Additionally, there is a problem in disks mapping logic: https://github.com/qoollo/bob/blob/master/bob/src/hw_metrics_collector.rs#L39

It iterates over system disks, but in docker every attached volume has different mount point but same device id, thus the same disk added multiple times. We should invert iteration logic (our disks first) and find a better way of mapping (probably, check path as well)