scripts: add EC2 metadata service simulator

Run it like this:

  $ sudo scripts/ec2-simulator.py

The tool starts HTTP server which can be reached via standard cloud
meta-data service IP (169.254.169.254).

It needs to modify NAT rules and insert an IP address so it needs to be
run with "sudo".

You can set user data via command line arguments, eg:

  $ sudo scripts/ec2-simulator.py -f user-data.yaml

Signed-off-by: Tomasz Grabiec <tgrabiec@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>