btrfs-progs: Add simple python front end to the search ioctl

btrfs-progs: Add simple python front end to the search ioctl

This is a starting point for a debugfs style python interface using
the search ioctl.  For now it can only do one thing, which is to
print out all the extents in a file and calculate the compression ratio.

Over time it will grow more features, especially for the kinds of things
we might run btrfs-debug-tree to find out.  Expect the usage and output
to change dramatically over time (don't hard code to it).

Signed-off-by: Chris Mason <clm@fb.com>
Signed-off-by: David Sterba <dsterba@suse.cz>