Fix waf invocation on systems that default to python 3.
Fix waf invocation on systems that default to python 3.

pebble/pebble-tool,gregoiresage/pebble-tool,gregoiresage/pebble-tool,gregoiresage/pebble-tool,pebble/pebble-tool,pebble/pebble-tool,gregoiresage/pebble-tool,pebble/pebble-tool