tests: describe turing.skip in README.md

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
contrib/nitester: use turing skip list

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
contrib/nitester: each worker us its own copy of the Nit repository

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
nitester-wrapper: only compile nitg and nitester on the host processor

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
nitester-wrapper: fix set -x

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
less blacklist