improving check_write_disk.py

Making the check discover all mount points, instead of just
working with the root disk.
Revert "improving check_write_disk.py"

This reverts commit 1f0cd7da2d4edbfc525b017a186b27871656b7e4.
improving check_write_disk.py

Making the check discover all mount points, instead of just
working with the root disk.
Merge pull request #5 from Knewton/check_write_disk

Check write disk