lib/mnit: frame_core is not abstract

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
examples: fix mnit_ballz and shoot for latest android.nit

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
tests: add mnit_linux to exec skip with other mnit projects

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
tests: skip mnit in niti as does nitg-g

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