tools/read-dependencies tools/read-version: rewrite in python

This just does python rewrites of these tools that were shell or sed or
grep.  Clearly the user of cloud-init has python, but it turns out that
getting sane versions of sed or grep on different unixes is less than
simple.
cc_resizefs: figure out what /dev/root means via kernel cmdline

If mount_info says that the root filesystem is on /dev/root and
/dev/root does not exist, then we'll try to glean that information
from the linux kernel cmdline.

This situation occurs at least when you boot without an initramfs
for the current ppc64el cloud images:
 qemu-system-ppc64 ... -kernel my.kernel -append 'root=/dev/sda'

When doing that, /proc/1/mountinfo will say '/dev/root' for '/'.