scripts: use EC2 tools from PATH

I don't have EC2_HOME set, I don't even know should I set it to, so
the scripts failed but all these tools seem to be on path after
installing releant packages (Ubuntu).

I'm not sure if that's the case for Fedora too.

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