tests: Use python2 explicitly
tests: Use python2 explicitly

Signed-off-by: Jan Vesely <6a2ac3bd1a50b5b4969c0b358741eeb258bebe0c@gmail.com>
Reviewed-by: Yang Rong <78759e37dc7114caed18f74e7515c5cb519dbf6d@intel.com>

wdv4758h/beignet,wdv4758h/beignet,wdv4758h/beignet,wdv4758h/beignet,wdv4758h/beignet