Add migration stream analyzation script

This patch adds a python tool to the scripts directory that can read
a dumped migration stream if it contains the JSON description of the
device states. I constructs a human readable JSON stream out of it.

It's very simple to use:

  $ qemu-system-x86_64
    (qemu) migrate "exec:cat > mig"
  $ ./scripts/analyze_migration.py -f mig
Signed-off-by: NAlexander Graf <agraf@suse.de>
Signed-off-by: NAmit Shah <amit.shah@redhat.com>
Signed-off-by: NJuan Quintela <quintela@redhat.com>