Add execute bit back to scripts/tracetool.py

Add execute bit back to scripts/tracetool.py

Commit a81df1b68b65 ("libqemuutil, qapi, trace: convert to meson")
removed it without explanation and it is useful to be able to run a
script without having to figure out which interpreter to use.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20200923103620.1980151-1-anthony.perard@citrix.com>