Fix inode usage calculation to use filepath.Walk instead of executing an
external find. Also calculate the disk usage while at it so we also get
rid of the external dependency of `nice` and `du`. (#95172)
This is similar to what cadvisor does since commit
046818d64c
This solves three problems:
- Counts number of inodes correct when there are hardlinks (#96114)
- Makes kubelet work without GNU findutils (#95186)
- Makes kubelet work without GNU coreutils (#95172)