To make the button command useful in a shell script it should return the
status of the button:

* 0 (true) - pressed, on
* 1 (false) - not pressed, off

The button command takes only one argument. Correct maxargs.

Adjust the Python unit test.
Signed-off-by: NHeinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: NPhilippe Reynes <philippe.reynes@softathome.com>